U.S. patent application number 13/030555 was filed with the patent office on 2011-08-25 for video processing circuit, liquid crystal display device, electronic apparatus, and video processing method.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Hiroyuki HOSAKA, Hidehito IISAKA.
Application Number | 20110205452 13/030555 |
Document ID | / |
Family ID | 44476218 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110205452 |
Kind Code |
A1 |
HOSAKA; Hiroyuki ; et
al. |
August 25, 2011 |
VIDEO PROCESSING CIRCUIT, LIQUID CRYSTAL DISPLAY DEVICE, ELECTRONIC
APPARATUS, AND VIDEO PROCESSING METHOD
Abstract
A video processing circuit replaces an applied voltage
designated by the video signal and applied to a first pixel with a
predetermined third voltage, in the case that the applied voltage
is lower than the third voltage, the first pixel is abutted on a
predetermined application boundary, and the first pixel is
surrounded by a risk boundary determined in accordance with a tilt
azimuth direction of the liquid crystal on at least two sides.
Inventors: |
HOSAKA; Hiroyuki;
(Matsumoto-shi, JP) ; IISAKA; Hidehito;
(Shiojiri-shi, JP) |
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
44476218 |
Appl. No.: |
13/030555 |
Filed: |
February 18, 2011 |
Current U.S.
Class: |
348/790 ;
345/212; 348/E3.016 |
Current CPC
Class: |
G09G 2320/0271 20130101;
G09G 2320/0209 20130101; G09G 2340/16 20130101; G09G 2310/0235
20130101; G09G 3/3611 20130101 |
Class at
Publication: |
348/790 ;
345/212; 348/E03.016 |
International
Class: |
G09G 5/00 20060101
G09G005/00; H04N 3/14 20060101 H04N003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2010 |
JP |
2010-039795 |
Claims
1. A video processing circuit adapted to supply a liquid crystal
panel, in which liquid crystal is sandwiched between a first
substrate provided with pixel electrodes corresponding respectively
to pixels and a second substrate provided with a common electrode,
and liquid crystal elements are mainly composed of the respective
pixel electrodes, the liquid crystal, and the common electrode,
with a video signal adapted to designate applied voltages
respectively to the liquid crystal elements pixel by pixel, and to
define the applied voltages to the respective liquid crystal
elements based on a processed video signal, the video processing
circuit comprising: a boundary detection section adapted to detect
a boundary between a first pixel having an applied voltage, which
is designated by the video signal input and is lower than a first
voltage, and a second pixel having an applied voltage, which is
designated by the video signal input and is one of equal to and
higher than a second voltage higher than the first voltage, in a
present frame and in a previous frame, which is one frame earlier
than the present frame, respectively; an application boundary
determination section adapted to determine an application boundary
obtained by eliminating an overlap between the boundary of the
present frame detected by the boundary detection section and the
boundary of the previous frame detected by the boundary detection
section from the boundary of the present frame; a risk boundary
detection section adapted to detect a risk boundary, which is a
part of a boundary between the first pixel having the applied
voltage, which is designated by the video signal input and is lower
than the first voltage, and the second pixel having the applied
voltage, which is designated by the video signal input and is
higher than the second voltage higher than the first voltage, and
is determined in accordance with a tilt azimuth direction of the
liquid crystal; a specifying section adapted to specify the first
pixel surrounded by the risk boundary on at least two sides out of
the first pixels abutting on the risk boundary; and a replacement
section adapted to replace the applied voltage designated by the
video signal input and applied to the liquid crystal element
corresponding to the first pixel, which is specified by the
specifying section, abuts on the application boundary determined by
the application boundary determination section, and has the applied
voltage designated by the video signal input lower than a
predetermined third voltage lower than the first voltage, with the
third voltage.
2. A video processing circuit adapted to supply a liquid crystal
panel, in which liquid crystal is sandwiched between a first
substrate provided with pixel electrodes corresponding respectively
to pixels and a second substrate provided with a common electrode,
and liquid crystal elements are mainly composed of the respective
pixel electrodes, the liquid crystal, and the common electrode,
with a video signal adapted to designate applied voltages
respectively to the liquid crystal elements pixel by pixel, and to
define the applied voltages to the respective liquid crystal
elements based on a processed video signal, the video processing
circuit comprising: a boundary detection section adapted to detect
a boundary between a first pixel having an applied voltage, which
is designated by the video signal input and is lower than a first
voltage, and a second pixel having an applied voltage, which is
designated by the video signal input and is one of equal to and
higher than a second voltage higher than the first voltage, in a
present frame and in a previous frame, which is one frame earlier
than the present frame, respectively; an application boundary
determination section adapted to determine an application boundary
obtained by eliminating an overlap between the boundary of the
present frame detected by the boundary detection section and the
boundary of the previous frame detected by the boundary detection
section from the boundary of the present frame; a risk boundary
detection section adapted to detect a risk boundary, which is a
part of a boundary between the first pixel having the applied
voltage, which is designated by the video signal input and is lower
than the first voltage, and the second pixel having the applied
voltage, which is designated by the video signal input and is
higher than the second voltage higher than the first voltage, and
is determined in accordance with a tilt azimuth direction of the
liquid crystal; a specifying section adapted to specify the first
pixel surrounded by the risk boundary on at least two sides out of
the first pixels abutting on the risk boundary; and a replacement
section adapted to replace the applied voltage designated by the
video signal input and applied to the liquid crystal element
corresponding to the second pixel, which abuts on the first pixel
specified by the specifying section, abuts on the application
boundary determined by the application boundary determination
section, and has the applied voltage designated by the video signal
input higher than the second voltage, with a predetermined fourth
voltage.
3. A video processing circuit according to claim 1, wherein a
replacement section adapted to replace the applied voltage
designated by the video signal input and applied to the liquid
crystal element corresponding to the second pixel, which abuts on
the first pixel specified by the specifying section, abuts on the
application boundary determined by the application boundary
determination section, and has the applied voltage designated by
the video signal input higher than the second voltage, with a
predetermined fourth voltage.
4. The video processing circuit according to claim 1, wherein the
replacement section replaces the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the first pixels, which are specified by the specifying
section, and are placed consecutively to at least one first pixel
abutting on the application boundary determined by the application
boundary determination section toward a side opposite to the
application boundary, with the predetermined third voltage.
5. The video processing circuit according to claim 2, wherein the
replacement section replaces the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the second pixels, which abut on at least one first pixel
specified by the specifying section, and are placed consecutively
to at least one second pixel abutting on the application boundary
determined by the application boundary determination section toward
a side opposite to the application boundary, with the predetermined
fourth voltage.
6. The video processing circuit according to claim 3, wherein the
replacement section replaces the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the first pixels, which are specified by the specifying
section, and are placed consecutively to at least one first pixel
abutting on the application boundary determined by the application
boundary determination section toward a side opposite to the
application boundary, with the predetermined third voltage, and
replaces the applied voltage to the liquid crystal element
corresponding to each of a predetermined plural number of the
second pixels, which abut on at least one first pixel specified by
the specifying section, and are placed consecutively to at least
one second pixel abutting on the application boundary determined by
the application boundary determination section toward a side
opposite to the application boundary, with the predetermined fourth
voltage.
7. The video processing circuit according to claim 1, wherein the
tilt azimuth direction is a direction from one end of a long axis
of a liquid crystal molecule on a side of the pixel electrode
toward the other end of the liquid crystal molecule in a plan view
from the side of the pixel electrode toward the common
electrode.
8. The video processing circuit according to claim 2, wherein the
tilt azimuth direction is a direction from one end of a long axis
of a liquid crystal molecule on a side of the pixel electrode
toward the other end of the liquid crystal molecule in a plan view
from the side of the pixel electrode toward the common
electrode.
9. The video processing circuit according to claim 3, wherein the
tilt azimuth direction is a direction from one end of a long axis
of a liquid crystal molecule on a side of the pixel electrode
toward the other end of the liquid crystal molecule in a plan view
from the side of the pixel electrode toward the common
electrode.
10. A liquid crystal display device comprising a video processing
circuit according to claim 1.
11. A liquid crystal display device comprising a video processing
circuit according to claim 2.
12. A liquid crystal display device comprising a video processing
circuit according to claim 3.
13. An electronic apparatus comprising the liquid crystal display
device according to claim 10.
14. An electronic apparatus comprising the liquid crystal display
device according to claim 11.
15. An electronic apparatus comprising the liquid crystal display
device according to claim 12.
16. A video processing method adapted to supply a liquid crystal
panel, in which liquid crystal is sandwiched between a first
substrate provided with pixel electrodes corresponding respectively
to pixels and a second substrate provided with a common electrode,
and liquid crystal elements are mainly composed of the respective
pixel electrodes, the liquid crystal, and the common electrode,
with a video signal adapted to designate applied voltages
respectively to the liquid crystal elements pixel by pixel, and to
define the applied voltages to the respective liquid crystal
elements based on a processed video signal, the video processing
method comprising: (a) detecting a boundary between a first pixel
having an applied voltage, which is designated by the video signal
input and is lower than a first voltage, and a second pixel having
an applied voltage, which is designated by the video signal input
and is one of equal to and higher than a second voltage higher than
the first voltage, in a present frame and in a previous frame,
which is one frame earlier than the present frame, respectively;
(b) determining an application boundary obtained by eliminating an
overlap between the boundary of the present frame detected in step
(a) and the boundary of the previous frame detected in step (a)
from the boundary of the present frame; (c) detecting a risk
boundary, which is a part of a boundary between the first pixel
having the applied voltage, which is designated by the video signal
input and is lower than the first voltage, and the second pixel
having the applied voltage, which is designated by the video signal
input and is higher than the second voltage higher than the first
voltage, and is determined in accordance with a tilt azimuth
direction of the liquid crystal; (d) specifying the first pixel
surrounded by the risk boundary on at least two sides out of the
first pixels abutting on the risk boundary; and (e) replacing the
applied voltage designated by the video signal input and applied to
the liquid crystal element corresponding to the first pixel, which
is specified in step (d), abuts on the application boundary
determined in step (b), and has the applied voltage designated by
the video signal input lower than a predetermined third voltage
lower than the first voltage, with the third voltage.
17. A video processing method adapted to supply a liquid crystal
panel, in which liquid crystal is sandwiched between a first
substrate provided with pixel electrodes corresponding respectively
to pixels and a second substrate provided with a common electrode,
and liquid crystal elements are mainly composed of the respective
pixel electrodes, the liquid crystal, and the common electrode,
with a video signal adapted to designate applied voltages
respectively to the liquid crystal elements pixel by pixel, and to
define the applied voltages to the respective liquid crystal
elements based on a processed video signal, the video processing
method comprising: (a) detecting a boundary between a first pixel
having an applied voltage, which is designated by the video signal
input and is lower than a first voltage, and a second pixel having
an applied voltage, which is designated by the video signal input
and is one of equal to and higher than a second voltage higher than
the first voltage, in a present frame and in a previous frame,
which is one frame earlier than the present frame, respectively;
(b) determining an application boundary obtained by eliminating an
overlap between the boundary of the present frame detected in step
(a) and the boundary of the previous frame detected in step (a)
from the boundary of the present frame; (c) detecting a risk
boundary, which is a part of a boundary between the first pixel
having the applied voltage, which is designated by the video signal
input and is lower than the first voltage, and the second pixel
having the applied voltage, which is designated by the video signal
input and is higher than the second voltage higher than the first
voltage, and is determined in accordance with a tilt azimuth
direction of the liquid crystal; (d) specifying the first pixel
surrounded by the risk boundary on at least two sides out of the
first pixels abutting on the risk boundary; and (f) replacing the
applied voltage designated by the video signal input and applied to
the liquid crystal element corresponding to the second pixel, which
abuts on the first pixel specified in step (d), abuts on the
application boundary determined in step (b), and has the applied
voltage designated by the video signal input higher than the second
voltage, with a predetermined fourth voltage.
18. A video processing method according to claim 10, wherein (f)
replacing the applied voltage designated by the video signal input
and applied to the liquid crystal element corresponding to the
second pixel, which abuts on the first pixel specified in step (d),
abuts on the application boundary determined in step (b), and has
the applied voltage designated by the video signal input higher
than the second voltage, with a predetermined fourth voltage.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a technology for reducing
failure on display in a liquid crystal panel.
[0003] 2. Related Art
[0004] Liquid crystal panels have a configuration in which one of a
pair of substrates has pixel electrodes corresponding to respective
pixels arranged in a matrix, the other substrate has a common
electrode disposed so as to be common to all of the pixels, and a
liquid crystal is sandwiched between each of the pixel electrodes
and the common electrode. In such a configuration, when a voltage
corresponding to a grayscale level is applied and held between each
of the pixel electrodes and the common electrode, the orientational
state of the liquid crystal is defined every pixel, and thus, the
transmittance or the reflectance is controlled. Therefore, it can
be said that in the configuration described above, only the
component out of the electrical field acting on the liquid crystal
molecules having a direction (or the opposite direction) from the
pixel electrode to the common electrode, namely the direction
perpendicular (vertical) to the surface of the substrate makes a
contribution to the display control.
[0005] Incidentally, as the pixel pitch of the liquid crystal panel
is narrowed due to miniaturization and improvement in definition,
an electric field generated between the pixel electrodes adjacent
to each other, namely the electrical field in a direction (lateral
direction) parallel to the surface of the substrate, is generated,
and further the influence thereof is becoming nonnegligible. When a
lateral electrical field is applied to the liquid crystal to be
driven by an electrical field in a vertical direction such as a
vertical alignment (VA) liquid crystal or a Twisted Nematic (TN)
liquid crystal, there arises a problem that orientation failure
(reverse tilt domain) of the liquid crystal is caused to thereby
cause failure on display.
[0006] In order for reducing the influence of the reverse tilt
domain, there are proposed a technology (see, e.g., JP-A-6-34965,
FIG. 1) of devising a structure of a liquid crystal panel such as
to define the shape of the light blocking layer (an opening
section) corresponding to the pixel electrode, a technology (see,
e.g., JP-A-2009-69608, FIG. 2) of clipping the video signal equal
to or higher than a set value when the average brightness value
obtained from the video signal is equal to or lower than a
threshold value under the determination that the reverse tilt
domain is generated, and so on.
[0007] However, the technology of reducing the reverse tilt domain
by the structure of the liquid crystal panel has disadvantages that
the aperture rate is apt to be lowered, and that the technology is
not applicable to the liquid crystal panels having already been
manufactured without devising the structure. On the other hand, the
technology of clipping the video signal equal to or higher than the
set value has a disadvantage that the brightness of the image
displayed is limited uniformly to the set value.
SUMMARY
[0008] An advantage of some aspects of the invention is to provide
a technology for reducing the reverse tilt domain while solving the
problems described above.
[0009] According to an aspect of the invention, there is provided a
video processing circuit adapted to supply a liquid crystal panel,
in which liquid crystal is sandwiched between a first substrate
provided with pixel electrodes corresponding respectively to pixels
and a second substrate provided with a common electrode, and liquid
crystal elements are mainly composed of the respective pixel
electrodes, the liquid crystal, and the common electrode, with a
video signal adapted to designate applied voltages respectively to
the liquid crystal elements pixel by pixel, and to define the
applied voltages to the respective liquid crystal elements based on
a processed video signal, the video processing circuit including a
boundary detection section adapted to detect a boundary between a
first pixel having an applied voltage, which is designated by the
video signal input and is lower than a first voltage, and a second
pixel having an applied voltage, which is designated by the video
signal input and is one of equal to and higher than a second
voltage higher than the first voltage, in a present frame and in a
previous frame, which is one frame earlier than the present frame,
respectively, an application boundary determination section adapted
to determine an application boundary obtained by eliminating an
overlap between the boundary of the present frame detected by the
boundary detection section and the boundary of the previous frame
detected by the boundary detection section from the boundary of the
present frame, a risk boundary detection section adapted to detect
a risk boundary, which is a part of a boundary between the first
pixel having the applied voltage, which is designated by the video
signal input and is lower than the first voltage, and the second
pixel having the applied voltage, which is designated by the video
signal input and is higher than the second voltage higher than the
first voltage, and is determined in accordance with a tilt azimuth
direction of the liquid crystal, a specifying section adapted to
specify the first pixel surrounded by the risk boundary on at least
two sides out of the first pixels abutting on the risk boundary,
and a replacement section adapted to replace the applied voltage
designated by the video signal input and applied to the liquid
crystal element corresponding to the first pixel, which is
specified by the specifying section, abuts on the application
boundary determined by the application boundary determination
section, and has the applied voltage designated by the video signal
input lower than a predetermined third voltage lower than the first
voltage, with the third voltage.
[0010] It should be noted that the replacement section can have a
configuration of replacing the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the first pixels, which are specified by the specifying
section, and are placed consecutively to at least one first pixel
abutting on the application boundary determined by the application
boundary determination section toward a side opposite to the
application boundary, with the predetermined third voltage.
[0011] Further, according to another aspect of the invention, there
is provided a video processing circuit adapted to supply a liquid
crystal panel, in which liquid crystal is sandwiched between a
first substrate provided with pixel electrodes corresponding
respectively to pixels and a second substrate provided with a
common electrode, and liquid crystal elements are mainly composed
of the respective pixel electrodes, the liquid crystal, and the
common electrode, with a video signal adapted to designate applied
voltages respectively to the liquid crystal elements pixel by
pixel, and to define the applied voltages to the respective liquid
crystal elements based on a processed video signal, the video
processing circuit including a boundary detection section adapted
to detect a boundary between a first pixel having an applied
voltage, which is designated by the video signal input and is lower
than a first voltage, and a second pixel having an applied voltage,
which is designated by the video signal input and is one of equal
to and higher than a second voltage higher than the first voltage,
in a present frame and in a previous frame, which is one frame
earlier than the present frame, respectively, an application
boundary determination section adapted to determine an application
boundary obtained by eliminating an overlap between the boundary of
the present frame detected by the boundary detection section and
the boundary of the previous frame detected by the boundary
detection section from the boundary of the present frame, a risk
boundary detection section adapted to detect a risk boundary, which
is a part of a boundary between the first pixel having the applied
voltage, which is designated by the video signal input and is lower
than the first voltage, and the second pixel having the applied
voltage, which is designated by the video signal input and is
higher than the second voltage higher than the first voltage, and
is determined in accordance with a tilt azimuth direction of the
liquid crystal, a specifying section adapted to specify the first
pixel surrounded by the risk boundary on at least two sides out of
the first pixels abutting on the risk boundary, and a replacement
section adapted to replace the applied voltage designated by the
video signal input and applied to the liquid crystal element
corresponding to the second pixel, which abuts on the first pixel
specified by the specifying section, abuts on the application
boundary determined by the application boundary determination
section, and has the applied voltage designated by the video signal
input higher than the second voltage, with a predetermined fourth
voltage.
[0012] It should be noted that the replacement section can have a
configuration of replacing the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the second pixels, which abut on at least one first pixel
specified by the specifying section, and are placed consecutively
to at least one second pixel abutting on the application boundary
determined by the application boundary determination section toward
a side opposite to the application boundary, with the predetermined
fourth voltage.
[0013] Further, according to still another aspect of the invention,
there is provided a video processing circuit adapted to supply a
liquid crystal panel, in which liquid crystal is sandwiched between
a first substrate provided with pixel electrodes corresponding
respectively to pixels and a second substrate provided with a
common electrode, and liquid crystal elements are mainly composed
of the respective pixel electrodes, the liquid crystal, and the
common electrode, with a video signal adapted to designate applied
voltages respectively to the liquid crystal elements pixel by
pixel, and to define the applied voltages to the respective liquid
crystal elements based on a processed video signal, the video
processing circuit including a boundary detection section adapted
to detect a boundary between a first pixel having an applied
voltage, which is designated by the video signal input and is lower
than a first voltage, and a second pixel having an applied voltage,
which is designated by the video signal input and is one of equal
to and higher than a second voltage higher than the first voltage,
in a present frame and in a previous frame, which is one frame
earlier than the present frame, respectively, an application
boundary determination section adapted to determine an application
boundary obtained by eliminating an overlap between the boundary of
the present frame detected by the boundary detection section and
the boundary of the previous frame detected by the boundary
detection section from the boundary of the present frame, a risk
boundary detection section adapted to detect a risk boundary, which
is a part of a boundary between the first pixel having the applied
voltage, which is designated by the video signal input and is lower
than the first voltage, and the second pixel having the applied
voltage, which is designated by the video signal input and is
higher than the second voltage higher than the first voltage, and
is determined in accordance with a tilt azimuth direction of the
liquid crystal, a specifying section adapted to specify the first
pixel surrounded by the risk boundary on at least two sides out of
the first pixels abutting on the risk boundary, and a replacement
section adapted to replace the applied voltage designated by the
video signal input and applied to the liquid crystal element
corresponding to the first pixel, which is specified by the
specifying section, abuts on the application boundary determined by
the application boundary determination section, and has the applied
voltage designated by the video signal input lower than a
predetermined third voltage lower than the first voltage, with the
third voltage, and to replace the applied voltage designated by the
video signal input and applied to the liquid crystal element
corresponding to the second pixel, which abuts on the first pixel
specified by the specifying section, abuts on the application
boundary determined by the application boundary determination
section, and has the applied voltage designated by the video signal
input higher than the second voltage, with a predetermined fourth
voltage.
[0014] It should be noted that the replacement section can have a
configuration of replacing the applied voltage to the liquid
crystal element corresponding to each of a predetermined plural
number of the first pixels, which are specified by the specifying
section, and are placed consecutively to at least one first pixel
abutting on the application boundary determined by the application
boundary determination section toward a side opposite to the
application boundary, with the predetermined third voltage, and
replacing the applied voltage to the liquid crystal element
corresponding to each of a predetermined plural number of the
second pixels, which abut on at least one first pixel specified by
the specifying section, and are placed consecutively to at least
one second pixel abutting on the application boundary determined by
the application boundary determination section toward a side
opposite to the application boundary, with the predetermined fourth
voltage.
[0015] According to the aspects of the invention described above,
since there is no need to make a change to the structure of the
liquid crystal panel, degradation in aperture ratio is never
caused, and it is also possible to apply the invention to the
liquid crystal panels having already manufactured without devising
the structure.
[0016] Further, according to the above aspects of the invention,
since the applied voltage to the pixel abutting on the risk
boundary out of the pixels having a movement from the previous
frame as a result of analysis of the image is corrected, the number
of pixels to be corrected in the applied voltage can be reduced
compared to the configuration of replacing the dark pixels abutting
on the risk boundary without exception.
[0017] It should be noted that the invention can be recognized not
only as the video processing circuit, but can also be recognized as
a liquid crystal display device, an electronic apparatus including
the liquid crystal display device, and a video processing
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0019] FIG. 1 is a diagram showing a liquid crystal display device
to which a video processing circuit according to an embodiment of
the invention is applied.
[0020] FIG. 2 is a diagram showing an equivalent circuit of a
liquid crystal element in the liquid crystal display device.
[0021] FIG. 3 is a diagram showing a configuration of the video
processing circuit.
[0022] FIGS. 4A and 4B are diagrams showing display characteristics
in the liquid crystal display device.
[0023] FIGS. 5A and 5B are diagrams showing a display operation in
the liquid crystal display device.
[0024] FIGS. 6A and 6B are diagrams showing suppression of the
reverse tilt by the video processing circuit.
[0025] FIGS. 7A and 7B are explanatory diagrams of the initial
orientation when a VA type is adopted in a liquid crystal
panel.
[0026] FIGS. 8A through 8C are diagrams for explaining motions of
an image in the liquid crystal panel.
[0027] FIGS. 9A through 9C are explanatory diagrams of the reverse
tilt generated in the liquid crystal panel.
[0028] FIGS. 10A through 10C are diagrams for explaining motions of
an image in the liquid crystal panel.
[0029] FIGS. 11A through 11C are explanatory diagrams of the
reverse tilt generated in the liquid crystal panel.
[0030] FIGS. 12A and 12B are explanatory diagrams of the reverse
tilt generated in the liquid crystal panel.
[0031] FIG. 13 is a diagram showing a process in the video
processing circuit.
[0032] FIG. 14 is a diagram showing the process in the video
processing circuit.
[0033] FIGS. 15A through 15C are explanatory diagrams of processed
orientation in the case of setting a tilt azimuth angle to 0
degree.
[0034] FIG. 16 is an explanatory diagram of the reverse tilt
generated at the tilt azimuth angle of 0 degree.
[0035] FIG. 17 is an explanatory diagram of the reverse tilt
generated at the tilt azimuth angle of 0 degree.
[0036] FIG. 18 is a diagram showing a displacement process at the
tilt azimuth angle of 0 degree.
[0037] FIGS. 19A and 19B are explanatory diagrams of processed
orientation in the case of setting the tilt azimuth angle to 225
degrees.
[0038] FIG. 20 is a diagram showing the displacement process at the
tilt azimuth angle of 225 degrees.
[0039] FIG. 21 is a diagram showing another displacement process
(part 1) in the video processing circuit.
[0040] FIG. 22 is a diagram showing another displacement process
(part 2) in the video processing circuit.
[0041] FIG. 23 is a diagram showing another displacement process
(part 3) in the video processing circuit.
[0042] FIGS. 24A and 24B are explanatory diagrams of the initial
orientation when a TN method is adopted in the liquid crystal
panel.
[0043] FIGS. 25A through 25C are explanatory diagrams of the
reverse tilt generated in the liquid crystal panel.
[0044] FIGS. 26A through 26C are explanatory diagrams of the
reverse tilt generated in the liquid crystal panel.
[0045] FIGS. 27A and 27B are explanatory diagrams of the reverse
tilt generated in the liquid crystal panel.
[0046] FIG. 28 is a diagram showing a projector to which the liquid
crystal display device is applied.
DESCRIPTION OF AN EXEMPLARY EMBODIMENT
Embodiment
[0047] An embodiment of the invention will hereinafter be explained
with reference to the drawings. FIG. 1 is a block diagram showing
an overall configuration of a liquid crystal display device to
which a video processing circuit according to an embodiment of the
invention is applied.
[0048] As shown in this drawing, the liquid crystal display device
1 has a control circuit 10, a liquid crystal panel 100, a scan line
drive circuit 130, and a data line drive circuit 140. Among these
constituents, the control circuit 10 is supplied with a video
signal Vid-in from a higher-level device in sync with a sync signal
Sync. The video signal Vid-in is digital data for respectively
designating the grayscale levels of the pixels in the liquid
crystal panel 100, and is supplied in the order of the scan with a
vertical scan signal, a horizontal scan signal, and a dot clock
signal (which are not shown) included in the sync signal Sync. It
should be noted that although the video signal Vid-in designates
the grayscale levels of the respective pixels, there is no
objection to saying that the video signal Vid-in is for designating
the applied voltages of the liquid crystal elements since the
applied voltages of the liquid crystal elements are determined in
accordance with the grayscale levels as described later.
[0049] The control circuit 10 is composed of a scan control circuit
20 and a video processing circuit 30. Among these circuits, the
scan control circuit 20 generates various types of control signals
to thereby control each section in sync with the sync signal Sync.
The video processing circuit 30, details of which will be described
later, is for processing the video signal Vid-in as a digital
signal to thereby output a data signal Vx as an analog signal.
[0050] The liquid crystal panel 100 has a configuration in which an
element substrate (a first substrate) 100a and an opposed substrate
(a second substrate) 100b are bonded to each other keeping a
constant gap, and a liquid crystal 105 to be driven by an
electrical field in a vertical direction is sandwiched in the
gap.
[0051] Among the surfaces of the element substrate 100a, an opposed
surface to the opposed substrate 100b is provided with a plurality
("m" rows) of scan lines 112 disposed along an X (lateral)
direction in the drawing and a plurality ("n" columns) of data
lines 114 disposed along a Y (vertical) direction while keeping
electrical isolation with each of the scan lines 112.
[0052] It should be noted that in the present embodiment in order
for distinguishing the scan lines 112 from each other, the scan
lines 112 are respectively referred to as 1st, 2nd, 3rd, . . . ,
(m-1)-th, and m-th scan lines in sequence from the top in the
drawing in some cases. Similarly, in order for distinguishing the
data lines 114 from each other, the data lines 114 are respectively
referred to as 1st, 2nd, 3rd, . . . , (n-1)-th, and n-th scan lines
in sequence from the left in the drawing in some cases.
[0053] The element substrate 100a is further provided with sets of
an n-channel TFT 116 and a pixel electrode 118 having a rectangular
shape and a light transmissive property corresponding respectively
to intersections between the scan lines 112 and the data lines 114.
The gate electrode of the TFT 116 is connected to the scan line
112, the source electrode is connected to the data line 114, and
the drain electrode is connected to the pixel electrode 118.
[0054] Incidentally, among the surfaces of the opposed substrate
100b, the opposed surface to the element substrate 100a is provided
with a common electrode 108 having a light transmissive property
disposed on the entire surface. The common electrode 108 is
provided with a voltage LCcom by a circuit not shown in the
drawing.
[0055] It should be noted that in FIG. 1 the opposed surface of the
element substrate 100a is the side facing to the opposed substrate
100b. Therefore, the scan lines 112, the data lines 114, the TFTs
116, and the pixel electrodes 118 should be illustrated with broken
lines. However, in order for avoiding difficulty in understanding
the structure, these elements are all illustrated with solid
lines.
[0056] FIG. 2 is a diagram showing an equivalent circuit of the
liquid crystal panel 100. The liquid crystal panel 100 has a
configuration in which the liquid crystal elements 120 each having
the liquid crystal 105 sandwiched between the pixel electrode 118
and the common electrode 108 are arranged so as to correspond to
the intersections between the scan lines 112 and the data lines
114.
[0057] Further, although omitted in FIG. 1, an auxiliary capacitor
(a storage capacitor) 125 is provided in parallel to each of the
liquid crystal elements 120 in practice as shown in FIG. 2. The
auxiliary capacitor 125 has one end connected to the pixel
electrode 118, and the other end commonly connected to a
capacitance line 115. The capacitance line 115 is temporally kept
at a constant voltage.
[0058] In such a configuration, when the scan line 112 becomes in
an H level, the TFT 116 having the gate electrode connected to that
scan line becomes in an ON state to thereby connect the pixel
electrode 118 to the data line 114. Therefore, by supplying the
data line 114 with the data signal having a voltage corresponding
to the grayscale when the scan line 112 is in the H level, the data
signal is applied to the pixel electrode 118 via the TFT 116 thus
set to the ON state. When the scan line 112 becomes in an L level,
the TFT 116 becomes in an OFF state, and the voltage applied to the
pixel electrode is held by a capacitive property of the liquid
crystal element 120 and the auxiliary capacitor 125.
[0059] In the liquid crystal element 120, the molecular orientation
state of the liquid crystal 105 varies in accordance with an
electrical field generated between the pixel electrode 118 and the
common electrode 108. Therefore, the liquid crystal element 120
becomes to have a transmittance corresponding to the applied and
held voltage if the liquid crystal element 120 is of the
transmissive type.
[0060] Since in the liquid crystal panel 100 the transmittance
varies every liquid crystal element 120, the liquid crystal element
120 corresponds to the pixel. Further, the arrangement area of the
pixels corresponds to a display area 101. It should be noted that
in the present embodiment the VA type is adopted as the liquid
crystal 105, and there is adopted a normally black mode in which
the liquid crystal element 120 becomes in a black state when no
voltage is applied.
[0061] The scan line drive circuit 130 supplies the 1st, 2nd, 3rd,
. . . , and m-th scan lines 112 with scan signals Y1, Y2, Y3, . . .
, and Ym, respectively, in accordance with a control signal Yctr by
the scan control circuit 20. In detail, as shown in FIG. 5A, the
scan line drive circuit 130 selects the scan lines 112 in the order
of the 1st, 2nd, 3rd, . . . , (m-1)-th, and m-th rows throughout
the frame, and at the same time, sets the scan signal to the scan
line thus selected to a selection voltage V.sub.H (the H level)
while setting the scan signals to other scan lines to a
non-selection voltage V.sub.L (the L level).
[0062] It should be noted that the frame denotes a period in which
the video signal Vid-in corresponding to an exposure is supplied,
and if the frequency of the vertical scan signal included in the
sync signal Sync is 60Hz, the period of the frame is 16.7 ms, the
inverse of the frequency. In the present embodiment, since the 1st,
2nd, 3rd, . . . , and m-th scan lines 112 are selected in sequence
throughout the frame, the liquid crystal panel 100 is driven at the
same rate as the video signal Vid-in. Therefore, in the present
embodiment, the period necessary for making the liquid crystal
panel 100 display the image corresponding to one exposure is equal
to the frame.
[0063] The data line drive circuit 140 samples the data signal Vx
supplied from the video processing circuit 30 to the 1st through
n-th data lines 114 as data signals X1 through Xn in accordance
with the control signal Xctr by the scan control circuit 20.
[0064] It should be noted that in the present explanation the
voltages except the applied voltage to the liquid crystal element
120 take the ground potential not shown as the reference of the
voltage of zero unless otherwise specified. The applied voltage to
the liquid crystal element 120 corresponds to an electrical
potential difference between the voltage LCcom of the common
electrode 108 and the pixel electrode 118, and therefore needs to
be distinguished from other voltages. Further, in order for
preventing the deterioration in the liquid crystal 105 due to the
application of the direct current component, alternating-current
drive is performed on the liquid crystal element 120. In detail,
the applied voltage is applied to the pixel electrode 118 while
being switched alternately between a positive voltage higher than
the voltage Vcnt as the center of the amplitude and the negative
voltage lower than the voltage Vcnt every frame. In such
alternating-current drive, a plane reverse type for setting the
writing polarities of all of the liquid crystal elements 120 in the
same frame to be the same is adopted in the present embodiment. It
should be noted that it is conceivable that the voltage LCcom to be
applied to the common electrode 108 is approximately equal to the
voltage Vcnt.
[0065] In the present embodiment, the relationship between the
applied voltage (V) and the transmittance (T) of the liquid crystal
element 120 can be expressed by the V (voltage)-T (transmittance)
characteristics shown in FIG. 4A since the normally black mode of
the VA type is adopted in the liquid crystal 105. In order for
making the liquid crystal element 120 have the transmittance
corresponding to the grayscale level designated by the video signal
Vid-in, it should be sufficient to apply the voltage corresponding
to the grayscale level to the liquid crystal element.
[0066] However, if the applied voltage to the liquid crystal
element 120 is simply defined in accordance with the grayscale
level designated by the video signal Vid-in, failure on display due
to the reverse tilt domain occurs in some cases.
[0067] As shown in FIG. 6A, for example, the failure appears as a
kind of a trailing phenomenon that a pixel, which is located at the
left edge portion (trailing edge portion of a movement) of a black
pattern having consecutive black pixels, and should change from a
black pixel to a white pixel, does not change to the white pixel
due to generation of the reverse tilt domain when the black pattern
moves rightward on the background composed of the white pixels in
the image designated by the video signal Vid-in.
[0068] It should be noted that from a different viewpoint in FIG.
6A it can be said that when a white pattern having consecutive
white pixels moves rightward on the background composed of the
black pixels, the pixel, which is located at the right edge portion
(the leading edge of the movement) of the white pattern, and should
change from the black pixel to the white pixel, does not change to
the white pixel due to generation of the reverse tilt domain.
[0069] Further, in the drawing, only a part of the image is
extracted for the sake of convenience of explanation.
[0070] It is conceivable that it is one of the causes of the
failure on display due to the reverse tilt domain that the
orientation of the liquid crystal molecules is disturbed due to the
influence of the lateral electrical field when the liquid crystal
molecules sandwiched in the liquid crystal element 120 change from
an unstable state to the oriented state corresponding to the
applied voltage in accordance with the movement of the image, and
it becomes thereafter difficult for the liquid crystal molecules to
change to the oriented state corresponding to the applied
voltage.
[0071] Here, the case of being affected by the lateral electrical
field denotes the case in which the electrical potential difference
between the pixel electrodes adjacent to each other increases. This
is the case in which a dark pixel at the black level (or close to
the black level) and a bright pixel at the white level (or close to
the white level) are adjacent to each other in the image to be
displayed.
[0072] Among these pixels, the dark pixel is defined as a pixel of
the liquid crystal element 120 having the applied voltage in a
voltage range A equal to or higher than a voltage Vbk of the black
level in the normally black mode and lower than a voltage Vth1 (a
first voltage). Further, the transmittance range (the grayscale
range) of the liquid crystal element having the applied voltage to
the liquid crystal element in the voltage range A is assumed to be
"a" for the sake of convenience.
[0073] Then, the bright pixel is defined as a liquid crystal
element 120 having the applied voltage in a voltage range B equal
to or higher than a voltage Vth2 (a second voltage) and equal to or
lower than a white level voltage Vwt in the normally black mode.
The transmittance range (the grayscale range) of the liquid crystal
element having the applied voltage to the liquid crystal element in
the voltage range B is assumed to be "b" for the sake of
convenience.
[0074] It should be noted that in some cases it is conceivable that
in the normally black mode, the voltage Vth1 is an optical
threshold voltage for setting the relative transmittance of the
liquid crystal element to 10%, and the voltage Vth2 is an optical
saturation voltage for setting the relative transmittance of the
liquid crystal element to 90%.
[0075] Incidentally, the case in which the liquid crystal molecules
are in the unstable state denotes the case in which the applied
voltage to the liquid crystal element is lower than a voltage Vc (a
third voltage). In the case in which the applied voltage to the
liquid crystal element is lower than Vc, since the restraining
force of the vertical electrical field caused by the applied
voltage is weaker than the restraining force due to the oriented
film, the orientation state of the liquid crystal molecules are
easily disturbed by a tiny external factor. Further, this is
because it is apt to take time to respond to the applied voltage if
the liquid crystal molecules try to tilt in response to the applied
voltage when the applied voltage thereafter exceeds the voltage Vc.
Conversely, if the applied voltage is equal to or higher than the
voltage Vc, the liquid crystal molecules start to tilt (start to
vary the transmittance) in accordance with the applied voltage, and
therefore, it can be said that the orientation state of the liquid
crystal molecules is in the stable state. In other words, the
voltage Vc is in a relationship with the voltage Vth1 defined by
the transmittance in which the voltage Vc is lower than the voltage
Vth1.
[0076] According to the thought described above, it can be said
that the pixel, in which the liquid crystal molecules have been in
the unstable state before the change, is in a situation in which
the reverse tilt domain can easily be caused by the influence of
the lateral electrical field when the dark pixel and the bright
pixel become adjacent to each other due to the movement of the
image. It should be noted that when making a study taking the
initial orientation state of the liquid crystal molecules into
consideration, there are both of the case in which the reverse tilt
domain occurs and the case in which the reverse tilt domain does
not occur depending on the positional relationship between the dark
pixel and the bright pixel. Therefore, each of these cases will be
studied.
[0077] FIG. 7A is a diagram showing the 2.times.2 pixels adjacent
to each other in both of lateral and vertical directions in the
liquid crystal panel 100, and FIG. 7B is a simplified
cross-sectional diagram when breaking the liquid crystal panel 100
with a vertical plane including the line p-q shown in FIG. 7A, and
in particular a diagram showing the state of the liquid crystal
molecules.
[0078] It is assumed that as shown in these drawings, the liquid
crystal molecules of the VA type are initially oriented with the
tilt angle of .theta.a and the tilt azimuth angle of .theta.b (=45
degrees) in the state in which the electrical potential difference
(the applied voltage to the liquid crystal element) between the
pixel electrode 118 and the common electrode 108 is set to
zero.
[0079] Here, since the reverse tilt domain is caused by the lateral
electrical field between the pixel electrodes 118 as described
above, the behavior of the liquid crystal molecules on the element
substrate 100a side provided with the pixel electrodes 118 becomes
controversial. Therefore, the tilt azimuth angle and the tilt angle
of the liquid crystal molecules are defined with reference to the
side of the pixel electrodes 118 (the element substrate 100a).
[0080] In detail, as shown in FIG. 7B, the tilt angle .theta.a is
defined as an angle which the long axis Sa of the liquid crystal
molecule forms with reference to the normal line Sv of the
substrate when the long axis Sa tilts around one of the ends of the
long axis Sa located on the side of the pixel electrode 118 so that
the other of the ends located on the side of the common electrode
108 rotates. Incidentally, the tilt azimuth angle .theta.b is
defined as an angle formed by a plane normal to the substrate (the
normal plane including the line p-q) including the long axis Sa and
the normal line Sv of the substrate with reference to a plane
normal to the substrate along the Y direction as the arranging
direction of the data lines 114. It should be noted that the tilt
azimuth angle .theta.b is defined as an angle obtained by defining
the rotational angle from the upward direction in the drawing (the
opposite direction to the Y direction) to the direction (the upper
right direction in FIG. 7A) starting from one of the ends of the
long axis of the liquid crystal molecule toward the other of the
ends in clockwise in a plan view from the side of the pixel
electrode 118 toward the common electrode 108.
[0081] Further, it is assumed that similarly in a plan view from
the side of the pixel electrode 118, the direction (the upper right
direction in FIG. 7A) from one end of the liquid crystal molecule
on the pixel electrode side toward the other end thereof is
referred to as a downstream side of the tilt azimuth direction for
the sake of convenience, and in contrast, the direction (the lower
left direction) from the other end toward the one end is referred
to as an upstream side of the tilt azimuth direction for the sake
of convenience.
[0082] In the liquid crystal panel 100 using the liquid crystal 105
having such initial orientation, attention is focused on four
pixels of "2.times.2" surrounded by the broken lines as shown in
FIG. 8A, for example. FIG. 8A shows the case in which a pattern
composed of the pixels (black pixels) at the black level moves in
the upper right direction by one pixel every frame on the
background of the area composed of the pixels (white pixels) at the
white level. In this case, as shown in FIG. 9A, the state of the
four pixels of 2.times.2 changes from the state in which all of the
pixels are black in the (n-1)-th frame to the state in which the
lower left pixel alone is the white pixel in the n-th frame.
[0083] As described above, in the normally black mode the applied
voltage, namely the electrical potential difference between the
pixel electrode 118 and the common electrode 108, is higher in the
white pixel than in the black pixel. Therefore, in the lower left
pixel to be changed from black to white, the liquid crystal
molecules are biased to tilt in the normal direction (the
horizontal direction to the substrate surface) to the electrical
field direction from the state illustrated with solid lines to the
state illustrated with broken lines as shown in FIG. 9B.
[0084] However, the electrical potential difference generated in
the gap between the pixel electrode 118 (Wt) of the white pixel and
the pixel electrode 118 (Bk) of the black pixel is comparable to
the electrical potential difference generated between the pixel
electrode 118 (Wt) of the white pixel and the common electrode 108,
and moreover, the gap between the pixel electrodes is narrower than
the gap between the pixel electrode 118 and the common electrode
108. Therefore, in comparison in the intensity of the electrical
field, the lateral electrical field generated in the gap between
the pixel electrode 118 (Wt) and the pixel electrode 118 (Bk) is
stronger than the vertical electrical field generated between the
pixel electrode 118 (Wt) and the common electrode 108.
[0085] Since the lower left pixel has been the black pixel with the
liquid crystal molecules in the unstable state in the (n-1)-th
frame, it takes time until the liquid crystal molecules tilt in
accordance with the intensity of the vertical electrical field. On
the other hand, the lateral electrical field from the pixel
electrode 118 (Bk) adjacent thereto is stronger than the vertical
electrical filed caused by the application of the voltage in the
white level to the pixel electrode 118 (Wt). Therefore, in the
pixel to be changed to the white pixel, as shown in FIG. 9B, the
liquid crystal molecules Rv located on the side adjacent to the
black pixel become in the reverse tilt state temporally prior to
other liquid crystal molecules biased to tilt in accordance with
the vertical electrical field.
[0086] The liquid crystal molecules Rv having become in the reverse
tilt state earlier affect negatively the motion of other liquid
crystal molecules biased to tilt in the direction parallel to the
substrate as illustrated with the broken lines in accordance with
the vertical electrical field. Therefore, the area where the
reverse tilt occurs in the pixel to be changed to the white pixel
spreads across a wide area beyond the gap between the pixel to be
changed to the white pixel and the black pixel so as to eat into
the pixel to be changed to the white pixel as shown in FIG. 9C.
[0087] It should be noted that the variation in the pattern shown
in FIG. 9A occurs not only in the example shown in FIG. 8A, but
also in the case in which the pattern composed of the black pixels
moves rightward by one pixel every frame as shown in FIG. 8B, or in
the case in which the pattern composed of the black pixels moves
upward by one pixel every frame as shown in FIG. 8C. Further, as in
the case of changing the viewpoint in the explanation of FIG. 6A,
the variation in the pattern also occurs in the case in which the
pattern composed of the white pixels moves in an upper right
direction, rightward, or upward by one pixel every frame on the
background of the area composed of the black pixels.
[0088] Then, attention is focused on the four pixels of 2.times.2
surrounded by the broken lines in the case in which the pattern
composed of the black pixels moves by one pixel every frame in a
lower left direction on the background of the area composed of the
white pixels as shown in FIG. 10A in the liquid crystal panel 100.
In this case, as shown in FIG. 11A, the state of the four pixels of
2.times.2 changes from the state in which all of the pixels are
black in the (n-1)-th frame to the state in which the upper right
pixel alone is the white pixel in the n-th frame.
[0089] Even after the change described above, the lateral
electrical field stronger than the vertical electrical field in the
gap between the pixel electrode 118 (Wt) and the common electrode
108 is generated in the gap between the pixel electrode 118 (Bk) of
the black pixel and the pixel electrode 118 (Wt) of the white
pixel. Due to the lateral electrical field, as shown in FIG. 11B,
in the black pixel, the liquid crystal molecules Rv located on the
side adjacent to the white pixel are varied in the orientation
temporally prior to other liquid crystal molecules biased to tilt
in accordance with the vertical electrical field, and thus become
in the reverse tilt state. However, since in the black pixel the
vertical electrical field does not vary from the (n-1)-th frame,
other liquid crystal molecules are hardly affected. Therefore, as
shown in FIG. 11C, the area where the reverse tilt occurs in the
pixel not changing from the black pixel is negligibly narrow
compared to the example shown in FIG. 9C.
[0090] Incidentally, in the upper right pixel out of the four
pixels of 2.times.2, which changes from black to white, since the
initial orientation direction of the liquid crystal molecules is
the direction hardly affected by the lateral electrical field, the
liquid crystal molecules becoming in the reverse tilt state hardly
exist even if the vertical electrical field is applied. Therefore,
in the upper right pixel, the liquid crystal molecules correctly
tilt in the direction parallel to the substrate as illustrated with
the broken lines in FIG. 11B as the intensity of the vertical
electrical field increases. As a result, since the upper right
pixel changes to the aimed white pixel, deterioration of the
display quality hardly occurs.
[0091] It should be noted that the variation in the pattern shown
in FIG. 11A occurs not only in the example shown in FIG. 10A, but
also in the case in which the pattern composed of the black pixels
moves leftward by one pixel every frame as shown in FIG. 10B, or in
the case in which the pattern composed of the black pixels moves
downward by one pixel every frame as shown in FIG. 10C.
[0092] Summarizing once the situation described with reference to
FIGS. 7A through 11C, it can be said that in the case of setting
the tilt azimuth angle .theta.b to 45 degrees in the VA type (in
the normally black mode), when focusing attention to a certain nth
frame, and all of the following requirements are fulfilled, the
reverse tilt domain is apt to occur in the nth frame.
[0093] That is, the reverse tilt is apt to occur in the bright
pixel:
[0094] 1. if the dark pixel and the bright pixel are adjacent to
each other, namely the pixel with a low applied voltage and the
pixel with a high applied voltage are adjacent to each other, to
thereby make the lateral electrical field strong focusing attention
to the n-th frame;
[0095] 2. if the bright pixel (with a high applied voltage) is
located on the lower left side, left side, or lower side
corresponding to the upstream side of the tilt azimuth direction in
the liquid crystal molecules with respect to the dark pixel (with a
low applied voltage) in the n-th frame; and
[0096] 3. if the pixel to be changed to the bright pixel in the
n-th frame has had the liquid crystal molecules in the unstable
state in the previous (n-1)-th frame as the previous frame.
[0097] In other words, the condition of generating the reverse tilt
domain in the bright pixel fulfilling the positional relationships
of the requirement 1 and the requirement 2 in the n-th frame is the
requirement 3, namely the liquid crystal molecules are in the
unstable state in the (n-1)-th frame as the previous frame.
[0098] It should be noted that the requirement 1 is substantially
equivalent to detecting the boundary on which the dark pixel and
bright pixels are adjacent to each other out of the image
represented by the video signal Vid-in. Further, the requirement 2
is equivalent to extracting the portion of the boundary thus
detected having the dark pixel located above the boundary and the
bright pixel located below the boundary, and the portion of the
boundary having the dark pixel located on the right of the boundary
and the bright pixel located on the left of the boundary. It should
be noted that it is assumed that the extracted portions of the
boundary thus detected are referred to as a "risk boundary" as
described later.
[0099] Incidentally, FIGS. 8A through 8C show the case in which the
four pixels of 2.times.2 are all the black pixels in the (n-1)-th
frame and have the lower left pixels only become the white pixels
in the subsequent n-th frame as an example. However, in general,
the motion appears not only in the (n-1)-th frame and the n-th
frame, but the similar motion also appears throughout several
anterior and posterior frames including these frames. Therefore, if
the reverse tilt domain occurs, it is conceivable that in the dark
pixel (the pixel provided with a white circular dot) having had the
liquid crystal molecules in the unstable state in the (n-1)-th
frame, the bright pixel borders the dark pixel on the lower left
side, the left side, or the lower side thereof in many cases as
shown in FIGS. 8A through 8C considering the motion of the image
pattern.
[0100] Therefore, in the case in which the dark pixel and the
bright pixel are adjacent to each other and the dark pixel is
located on the upper right side, the right side, or the upper side
with respect to the bright pixel in the image represented by the
video signal Vid-in in the previous (n-1)-th frame, if the voltage
with which the liquid crystal molecules do not become in the
unstable state is applied to the liquid crystal element
corresponding to the dark pixel, it might be possible to prevent
the reverse tilt from occurring in the n-th frame since the
requirement 3 is never fulfilled even if the requirement 1 and the
requirement 2 are fulfilled in the n-th frame due to the motion of
the image pattern.
[0101] Rephrasing the above using the risk boundary while setting
back the time reference as much as 1 frame, it denotes that if in
the n-th frame, on the boundary on which the dark pixel and the
bright pixel border each other in the image represented by the
video signal Vid-in, the portion of the boundary having the dark
pixel located on the upper side and the bright pixel located on the
lower side and the portion thereof having the dark pixel located on
the right and the bright pixel located on the left are detected as
the risk boundary, and the voltage with which the liquid crystal
molecules do not become in the unstable state is applied to the
liquid crystal element corresponding to the dark pixel abutting on
the risk boundary, the requirement 3 is never fulfilled even if the
requirement 1 and the requirement 2 are fulfilled in the subsequent
(n+1)-th frame. Therefore, it might be possible to prevent the
reverse tilt from occurring in the oncoming (n+1)-th frame.
[0102] However, applying the voltage with which the liquid crystal
molecules do not become in the unstable state to the liquid crystal
element corresponding to the dark pixel is nothing more or less
than generating display departure in which an image not based on
the video signal Vid-in is displayed in essence. Therefore, from
the viewpoint of reducing the pixels constituting the display
departure as described above as much as possible, the requirements
1 through 3 described above will be reconsidered.
[0103] As shown in FIG. 12A, in the case in which the four pixels
of 2.times.2 are all, for example, the black pixels (Bk) the
(n-1)-th frame, when the lower left pixel alone changes to the
white pixel (Wt) in the n-th frame, the reverse tilt occurs in the
white pixel as already explained with reference to FIGS. 9A through
9C. The reverse tilt in this case occurs on the upper side and the
right side of the white pixel as shown in the n-th frame of FIG. 9C
or FIG. 12A. This is because in the lower left white pixel there
are generated strong lateral electrical fields with the black pixel
located on the upper side, the black pixel located on the upper
right side, and the black pixel located on the right side,
respectively.
[0104] In the subsequent (n+1)-th frame, when the lower right pixel
(having the white pixel bordering on the right side) changes to the
white pixel due to the movement of the black pattern, the reverse
tilt occurs similarly in the lower right pixel on the upper side
and the right side thereof, and the reverse tilt area is linked
with the reverse tilt area having already occurred on the upper
side of the lower left pixel. Thus, the reverse tilt generation
area continues over a plurality of pixels, and as a result, it
becomes visually conspicuous.
[0105] Then, the case in which the lower left pixel and the upper
left pixel of the four pixels of 2.times.2 change to the white
pixels in the n-th frame, namely the case in which the left half
column thereof changes to the white pixels as shown in FIG. 12B
will be considered. In this case, in the lower left pixel (the
observed pixel) to be changed to the white pixel in the n-th frame,
the reverse tilt occurs on the upper right corner and the right
side thereof, but hardly occurs on the upper side as shown in n-th
frame of FIG. 12B. This is because in the observed pixel there are
generated the strong lateral electrical fields with the black pixel
located on the upper right side and the black pixel located on the
right side, but the lateral electrical field is hardly generated
with the bright pixel located on the upper side.
[0106] Further, although the reverse tilt occurs on the right side
of the observed pixel, on the ground that no lateral electrical
field is generated on the upper side, the width in the horizontal
direction of the reverse tilt generation area is also reduced
compared to the case shown in FIG. 12A in which the lateral
electrical field occurs on two sides (the upper side and the right
side).
[0107] Even if in the (n+1)-th frame the lower right pixel and the
upper right pixel of the four pixels of 2.times.2 become the white
pixels due to the rightward movement of the black pattern, the
reverse tilt generation area is not linked, but remains discrete,
and therefore never becomes visually conspicuous because the
reverse tilt extending in the horizontal direction (the X
direction) does not exist on the upper side.
[0108] It should be noted that although the case in which the lower
left pixel and the upper left pixel of the four pixels of 2.times.2
are changed to the bright pixels in the n-th frame is considered
here, the same can be applied also to the case in which the lower
left pixel and the lower right pixel change to the bright pixels,
namely the case in which the lower half row changes to the white
pixels.
[0109] As described above, even in the case in which the white
(bright) pixel fulfilling the positional relationship of the
requirement 1 and the requirement 2 in the n-th frame fulfills the
requirement 3, although the reverse tilt occurs, the influence
thereof is visually inconspicuous in some cases. In view of this
point, the requirement 2 described above will be amended as the
requirement 2a below.
[0110] That is, the clause of the requirement 2 is replaced with
the following clause.
[0111] "2a. if the bright pixel (with a high applied voltage) is
surrounded by the dark pixels (with a low applied voltage) located
on the upper side, the upper right side, and the right side
thereof, namely if the bright pixel is surrounded by the risk
boundary on the upper side and the right side in the n-th frame;
and"
[0112] Therefore, it results that the reverse tilt can be prevented
from occurring by the following measures taking the expression
using the risk boundary when setting back the time reference as
much as one frame while taking the requirements 1, 2a, and 3 into
consideration.
[0113] That is, in the n-th frame, in the boundary on which the
dark pixel and the bright pixel border each other, the portion of
the boundary having the dark pixel located on the upper side and
the bright pixel located on the lower side and the portion thereof
having the dark pixel located on the right side and the bright
pixel located on the left side are detected as the risk
boundary.
[0114] Further, it results that by applying the voltage with which
the liquid crystal molecules do not become in the unstable state to
the liquid crystal element of the dark pixel bordering the pixel
having the state changed from the dark pixel to the bright pixel in
the n-th frame and surrounded by the risk boundary on two sides
(the left side and the lower side) among the dark pixels abutting
on the risk boundary, the reverse tilt can be prevented from
occurring in the oncoming (n+1)-th frame.
[0115] In other words, the invention is to prevent the reverse tilt
domain from occurring while considering the state of the previous
frame in addition to the risk boundary in the correction of the
present frame.
[0116] Then, consideration will be given to how the liquid crystal
molecules can be prevented from becoming in the unstable state in
the dark pixel in the case in which the dark pixel and the bright
pixel border each other in the image represented by the video
signal Vid-in and the dark pixel is in the positional relationship
described above with the bright pixel in the n-th frame. As
described above, the case in which the liquid crystal molecules are
in the unstable state denotes the case in which the applied voltage
to the liquid crystal element is lower than the voltage Vc.
Therefore, it results that if the applied voltage to the liquid
crystal element designated by the video signal Vid-in is lower than
the voltage Vc in the dark pixel fulfilling the positional
relationship described above, it is sufficient to forcibly replace
the applied voltage with a voltage equal to or higher than the
voltage Vc and then apply it thereto.
[0117] Then, what value is preferable as the voltage to replace
with will be studied. If priority is given to the point that the
liquid crystal molecules are set in a more stable state when the
applied voltage is replaced with the voltage equal to or higher
than the voltage Vc and applied to the liquid crystal element in
the case in which the applied voltage designated by the video
signal Vid-in is lower than the voltage Vc, or to the point that
the reverse tilt domain is more surely prevented from occurring,
the higher voltage is more preferable. However, in the normally
black mode, the transmittance rises as the applied voltage to the
liquid crystal element is raised. Since the grayscale level
designated by the original video signal Vid-in corresponds to the
dark pixel, namely a rather low transmittance, raising the
replacement voltage leads to displaying a bright pixel not based on
the video signal Vid-in.
[0118] In contrast, if priority is given to the point that when
applying the voltage replaced so as to be equal to or higher than
the voltage Vc to the liquid crystal element, the variation in the
transmittance due to the replacement is prevented from being
perceived, it results that the voltage Vc, the lower limit, is
preferable.
[0119] As described above, what value should be taken as the
replacement voltage should be determined based on what has a higher
priority. Although in the present embodiment, the voltage Vc is
adopted as the replacement voltage giving priority to the point
that the variation in the transmittance due to the replacement is
prevented from being perceived, if priority is given to the other
point described above, it is not necessary to adopt the voltage
Vc.
[0120] It should be noted that the liquid crystal molecules in the
VA type take the orientation most approximate to the direction
perpendicular to the surface of the substrate when the applied
voltage to the liquid crystal element is zero. The voltage Vc is in
a range of the voltage of providing the liquid crystal molecules
with the initial tilt angle, and the liquid crystal molecules start
to tilt in response to application of this voltage.
[0121] The voltage Vc with which the liquid crystal molecules
become in the stable state is not simply be determined because the
voltage Vc is generally correlated with various parameters in the
liquid crystal panel. However, in the liquid crystal panel having
the gap between the pixel electrodes 118 narrower than the gap
(cell gap) between the pixel electrode 118 and the common electrode
108 as is the case of the present embodiment, the voltage Vc is
about 1.5 volt.
[0122] Therefore, since the 1.5 volt is the lower limit of the
replacement voltage, it results that the voltage equal to or higher
than this voltage is sufficient. Conversely, if the applied voltage
to the liquid crystal element is lower than 1.5 volt, the liquid
crystal molecules become in the unstable state.
[0123] The video processing circuit 30 shown in FIG. 1 is the
circuit for processing the video signal Vid-in based on such a
thought as described above to thereby prevent the reverse tilt
domain from occurring in the liquid crystal panel 100. Therefore,
the video processing circuit 30 will hereinafter be explained in
detail.
[0124] FIG. 3 is a block diagram showing a configuration of the
video processing circuit 30.
[0125] As shown in this drawing, the video processing circuit 30
has a correction section 300, a boundary detection section 302, a
storage section 306, an application boundary determination section
308, a risk boundary detection section 321, a specifying section
322, a delay circuit 312, and a D/A converter 316.
[0126] Among these constituents, the delay circuit 312 is for
accumulating the video signal Vid-in supplied from the higher-level
device, and then retrieving it after a predetermined time elapses
to output it as a video signal Vid-d, and is mainly composed of a
first-in first-out (FIFO) memory and a multistage latch circuit. It
should be noted that the accumulation and the retrieval in the
delay circuit 312 are controlled by the scan control circuit
20.
[0127] In the present embodiment, the boundary detection section
302 analyzes the image represented by the video signal Vid-in to
detect the boundary on which a pixel in a grayscale range "a" and a
pixel in a grayscale range "b" border each other, and then outputs
boundary information representing the boundary.
[0128] It should be noted that the boundary here strictly denotes
the portion where the pixel in the grayscale range "a" and the
pixel in the grayscale range "b" border each other. Therefore, the
portion where the pixel in the grayscale range "a" and the pixel in
the grayscale range "c" border each other, or the portion where the
pixel in the grayscale range "b" and the pixel in the grayscale
range "c" border each other, for example, is not treated as the
boundary. Further, since the video signal Vid-in (Vid-d) represents
the image to be displayed, the frame of the image represented by
the video signal Vid-in (Vid-d) is also referred to as a present
frame in some cases.
[0129] Incidentally, the storage section 306 is for storing the
information of the boundary output by the boundary detection
section 302, and then outputting the information of the boundary
thus stored after one frame elapses. Therefore, it is arranged that
the storage section 306 outputs the information of the boundary in
the frame previous to the present frame, the information of the
boundary of which is output from the boundary detection section
302. It should be noted that the storage and the output of
information in the storage section 306 are controlled by the scan
control circuit 20.
[0130] The application boundary determination section 308 is for
determining what is obtained by excluding portions of the boundary
of the present frame, which is detected by the boundary detection
section 302, identical to the boundary of the previous frame stored
in the storage section 306 from the boundary of the present frame
as an application boundary.
[0131] The risk boundary detection section 321 analyzes the image
represented by the video signal Vid-in to thereby perform first
detection and second detection. In detail, the risk boundary
detection section 321 respectively performs the first detection for
detecting the boundary on which the pixel in the grayscale range
"a" and the pixel in the grayscale range "b" border each other in a
vertical direction or a horizontal direction, and the second
detection for detecting the portion of the boundary thus detected
having the dark pixel located on the upper side and the bright
pixel located on the lower side, and the portion thereof having the
dark pixel located on the right side and the bright pixel located
on the left side as the risk boundary.
[0132] The specifying section 322 specifies the dark pixel
surrounded by the risk boundary on two sides, namely the left side
and the lower side, out of the dark pixels abutting on the risk
boundary output by the risk boundary detection section 321.
[0133] The correction section 300 has a discrimination section 310
and a selector 314.
[0134] Among these constituents, the discrimination section 310
discriminates whether or not the grayscale level of the pixel
represented by the video signal Vid-d delayed by the delay circuit
312 belongs to the grayscale range "a," the pixel abuts on the
application boundary determined by the application boundary
determination section 308, and the pixel is specified by the
specifying section 322.
[0135] Here, the discrimination section 310 sets the value of the
flag Q to be supplied to the selector 314 to "1" if the
discrimination result is "Yes," or sets the value of the flag Q to
"0" if the discrimination result is "No."
[0136] It should be noted that since the risk boundary detection
section 321 cannot detect the boundary throughout the image to be
displayed in the vertical or horizontal direction unless the video
signal corresponding to a plurality of rows has been stored, the
delay circuit 302 is provided for the purpose of adjusting the
supply timing of the video signal Vid-in from the higher-level
device. Therefore, since the timing of the video signal Vid-in
supplied from the higher-level device and the timing of the video
signal Vid-d supplied from the delay circuit 302 are different from
each other, the horizontal scanning period or the like is not
identical between the both signals in a strict sense. However, the
explanation will hereinafter be presented with no particular
discrimination.
[0137] Further, the accumulation of the video signal Vid-in or the
like in the risk boundary detection section 321 is controlled by
the scan control circuit 20.
[0138] The selector 312 is for replacing the video signal Vid-d
with a video signal with the grayscale level "c1" and then
outputting it as a video signal Vid-out if the grayscale level
designated by the video signal Vid-d designates a level darker than
"c1" in the case in which the value of the flag Q supplied from the
discrimination section 314 is "1."
[0139] It should be noted that if the value of the flag Q is "0,"
the selector 312 directly outputs the video signal Vid-d as the
video signal Vid-out without replacing grayscale level.
[0140] The D/A converter 316 converts the video signal Vid-out as a
digital data into a data signal Vx as an analog signal. It should
be noted that as described above since the plane reverse type is
adopted in the present embodiment, the polarity of the data signal
Vx is switched every time rewriting of one exposure is performed on
the liquid crystal panel 100.
[0141] According to the video processing circuit 30 described
above, if the pixel represented by the video signal Vid-d has the
grayscale level darker than "c1," abuts on the application
boundary, and is the dark pixel surrounded by the risk boundary on
the two sides, the value of the flag is set to "1," the grayscale
level of the dark pixel represented by the video signal Vid-d is
replaced with "c1," and then the video signal Vid-d is output as
the video signal Vid-out.
[0142] In contrast, if the pixel represented by the video signal
Vid-d does not abut on the application boundary, if it is not the
dark pixel abutting on the risk boundary, if it is the dark pixel
abutting on the risk boundary with only one side even though it
does abut on the risk boundary, or if a bright grayscale level
equal to or higher than "c1" is designated, the value of the flag Q
is set to "0," and therefore, the video signal Vid-d is output as
the video signal Vid-out without correcting the grayscale
level.
[0143] Then, the display operation of the liquid crystal display
device 1 will be explained. The video signal Vid-in is supplied
from the higher-level device throughout the frame in the pixel
order of (1st row, 1st column) through (1st row, n-th column), (2nd
row, 1st column) through (2nd row, n-th column), (3rd row, 1st
column) through (3rd row, n-th column), . . . , (m-th row, 1st
column) through (m-th row, n-th column). The video processing
circuit 30 performs, for example, the delay process and the
replacement process on the video signal Vid-in, and outputs the
result as the video signal Vid-out.
[0144] Here, when focusing attention on the horizontal effective
scanning period (Ha) in which the video signal Vid-out of the (1st
row, 1st column) through (1st row, n-th column) is output, the
video signal Vid-out is converted by the D/A converter 316 into the
data signal Vx having either one of positive or negative polarities
(e.g., the positive polarity here) as shown in FIG. 5B. The data
signal Vx is sampled by the data line drive circuit 140 on the data
lines 114 corresponding to the 1st through n-th columns as the data
signals X1 through Xn.
[0145] Incidentally, in the horizontal scanning period in which the
video signal Vid-out corresponding to the (1st row, 1st column)
through (1st row, n-th column) is output, the scan control circuit
20 controls the scan line drive circuit 130 to set only the scan
signal Yl to the H level. If the scan signal Y1 is in the H level,
the TFTs 116 on the 1st row become in the ON state, and therefore,
the data signals sampled on the data lines 114 are applied to the
pixel electrodes 118 via the TFTs 116 in the ON state,
respectively. Thus, the positive voltages corresponding to the
grayscale levels designated by the video signal Vid-out are written
into the liquid crystal elements of the (1st row, 1st column)
through (1st row, n-th column), respectively.
[0146] Subsequently, the video signal Vid-in corresponding to the
(2nd row, 1st column) through (2nd row, n-th column) is similarly
processed by the video processing circuit 30 and then output as the
video signal Vid-out, and at the same time, converted by the D/A
converter 316 into the positive data signal to be sampled by the
data line drive circuit 140 on the data lines 114 corresponding
respectively to the 1st through n-th columns.
[0147] In the horizontal scanning period in which the video signal
Vid-out corresponding to the (2nd row, 1st column) through (2nd
row, n-th column) is output, since the scan line drive circuit 130
sets only the scan signal Y2 to the H level, the data signals
sampled on the data lines 114 are applied to the pixel electrodes
118 via the TFTs 116 in the 2nd row in the ON state, respectively.
Thus, the positive voltages corresponding to the grayscale levels
designated by the video signal Vid-out are written into the liquid
crystal elements of the (2nd row, 1st column) through (2nd row,
n-th column), respectively.
[0148] Subsequently, substantially the same writing operation is
performed on each of the 3rd, 4th, . . . , and m-th rows, and thus
the voltages corresponding to the respective grayscale levels
designated by the video signal Vid-out are written into the
respective liquid crystal elements. Thus, it results that the
transmissive image defined by the video signal Vid-in is
formed.
[0149] In the subsequent frame, substantially the same writing
operation is performed except the fact that the video signal
Vid-out is converted into the negative data signal due to the
polarity reversal of the data signal.
[0150] FIG. 5B is a voltage waveform chart showing an example of
the data signal Vx in the case in which the video signal Vid-out
corresponding to the (1st row, 1st column) through (1st row, n-th
column) is output throughout the horizontal scanning period (H)
from the video processing circuit 30. Since the normally black mode
is adopted in the present embodiment, the data signal Vx takes a
higher voltage value (indicated by .uparw. in the drawing) with
respect to the amplitude center voltage Vcnt as the grayscale level
processed by the video processing circuit 30 becomes brighter in
the case of the positive polarity, while the data signal Vx takes a
lower voltage value (indicated by .dwnarw. in the drawing) with
respect to the amplitude center voltage Vcnt as the grayscale level
becomes brighter in the case of the negative polarity.
[0151] In detail, the voltage of the data signal Vx becomes the
voltage shifted from the reference voltage Vcnt as much as an
amount corresponding to the grayscale in a range from the voltage
Vw (+) corresponding to white to the voltage Vb (+) corresponding
to black in the case of the positive polarity, or in a range from
the voltage Vw (-) corresponding to white to the voltage Vb (-)
corresponding to black in the case of the negative polarity.
[0152] The voltage Vw (+) and the voltage Vw (-) are in a
symmetrical relationship with each other about the voltage Vcnt.
The voltage Vb (+) and the voltage Vb (-) are also in a symmetrical
relationship with each other about the voltage Vcnt.
[0153] It should be noted that FIG. 5B is for showing the voltage
waveform of the data signal Vx, which is different from the voltage
(the electrical potential difference between the pixel electrode
118 and the common electrode 108) to be applied to the liquid
crystal element 120. Further, the vertical scale of the voltage of
the data signal in FIG. 5B is expanded compared to the voltage
waveforms of the scan signals in FIG. 5A.
[0154] Subsequently, a specific example of a correction process by
the video processing circuit 30 shown in FIG. 3 will be explained
taking the case as an example, in which (a part of) the image
represented by the video signal Vid-in is an image for displaying a
pattern of the black (dark) pixels having the liquid crystal
molecules in the unstable state on the background of the white
(bright) pixels in the grayscale range "b" as shown in the part 1
of FIG. 13.
[0155] In the case in which the image represented by the video
signal Vid-in of the present frame is as shown in the part 2 of
FIG. 13, for example, and the image represented by the video signal
of the previous frame is, for example, as shown in the part 1 of
FIG. 13, the boundary of the image of the previous frame detected
by the boundary detection section 302 and then stored in the
storage section 306 and the boundary of the image of the present
frame detected by the boundary detection section 302 are as shown
in the part 3 of FIG. 13. Therefore, the application boundary
determined by the application boundary determination section 308
becomes as shown in the part 4 of FIG. 14.
[0156] Further, in the case in which the image of the present frame
represented by the video signal Vid-in is as shown in the part 2 of
FIG. 13, the risk boundary detected by the risk boundary detection
section 321 becomes as shown in the part 5 of FIG. 14.
[0157] In other words, in the boundary (not shown) on which the
dark pixel and the bright pixel border each other, the portion
having the dark pixel located on the upper side of the boundary and
the bright pixel located on the lower side of the boundary, and the
portion having the dark pixel located on the right side of the
boundary and the bright pixel located on the left side of the
boundary become the risk boundary.
[0158] The specifying section 322 specifies the dark pixel
surrounded by the risk boundary on two sides (the left side and the
lower side) out of the dark pixels abutting on the risk boundary.
In the example shown in the part 2 of FIG. 13, the dark pixels
surrounded on two sides are three pixels provided with white
circles in the part 5 of FIG. 14.
[0159] Regarding the dark (black) pixels having the grayscale level
belonging to the grayscale range "a," abutting on the application
boundary shown in the part 4 of FIG. 14, and surrounded by the risk
boundary on two sides among the dark pixels provided with the white
circles in the part 5 of FIG. 14, since the discrimination result
in the discrimination section 310 is set to "Yes," and the
grayscale level is replaced with the grayscale level "c1" by the
selector 312, the image thus processed becomes as shown in the part
6 of FIG. 14.
[0160] It should be noted that even in the case in which the dark
pixel has the grayscale level belonging to the grayscale range "a,"
and abuts on the risk boundary, if the pixel does not abut on the
application boundary (the pixel located at the third row from the
top and the fifth column from the right in the part 5 of FIG. 14),
the discrimination result in the discrimination section 310 becomes
"No," and the grayscale level is not replaced by the selector
312.
[0161] Therefore, even if the image represented by the video signal
Vid-in includes the part changing from the black pixel to the white
pixel due to the left side portion of the pattern composed of the
black pixels moving one pixel rightward on the background of the
white pixels as shown in the part 1 and the part 2 of FIG. 13, for
example, in the liquid crystal panel 100, the black pixel does not
change from the state in which the liquid crystal molecules are in
the unstable state directly to the white pixel, but changes to the
white pixel after once passing through the state in which the
liquid crystal molecules are forcibly set to the stable state due
to the application of the voltage Vc corresponding to the grayscale
level "c1" as shown in FIG. 6B. Therefore, the reverse tilt domain
can be prevented from occurring. It should be noted that although
not particularly illustrated, the same can be applied to the case
in which the black pattern moves in the upper right direction or
the upward direction.
[0162] Further, regarding the black pixel abutting on the risk
boundary but not abutting on the pixel with the state having
changed from the previous frame, namely the black pixel abutting on
the risk boundary but not abutting on the application boundary,
since the grayscale level is not replaced by the selector 312 with
the grayscale level "c1," the portion where the display not based
on the video signal Vid-in occurs can be reduced compared to the
configuration of replacing the dark pixels abutting on the risk
boundary without exception.
[0163] Further, it becomes possible to prevent the area where the
reverse tilt easily occurs from being continuous due to the
movement of the black pixel.
[0164] Further, since in the present embodiment the video signal
equal to or higher than a set value is not clipped without
exception, the harmful influence exerted on the contrast ratio by
setting unavailable voltage range is eliminated.
[0165] Further, since there is no need to make a change to the
structure of the liquid crystal panel 100, degradation in aperture
ratio is never caused, and it is also possible to apply the
invention to the liquid crystal panels having already manufactured
without devising the structure.
Another Example of Tilt Azimuth Angle
[0166] In the embodiment described above, the case in which the
tilt azimuth angle .theta.b is 45 degrees in the normally black
mode of the VA type is explained. Then, an example having the tilt
azimuth angle .theta.b other than 45 degrees will hereinafter be
explained.
Tilt Azimuth Angle: 0 Degree
[0167] Firstly, the case in which the tilt azimuth angle .theta.b
is equal to 0 degree as shown in FIG. 15A will be explained. In
this case, when the liquid crystal molecules are in the unstable
state in the observed pixel and all of the peripheral pixels, and
the observed pixel alone changes to the bright pixel (Wt), the
reverse tilt occurs in the observed pixel on the upper side, the
right side, and the left side of the bright pixel as shown in FIG.
15C.
[0168] Since the upper side of the bright pixel is the downstream
side of the tilt azimuth direction in the liquid crystal molecules,
the liquid crystal molecules located on the side bordering the
upper black pixel become in the reverse tilt state due to the
lateral electrical field caused with the upper dark pixel
temporally prior to other liquid crystal molecules biased to tilt
with the vertical electrical field.
[0169] On the upper right corner of the bright pixel, the lateral
electrical field in an RU direction is generated in FIG. 15A due to
the adjacency with the upper right black pixel. In the case in
which the tilt azimuth angle .theta.b is 0 degree, when cutting the
liquid crystal panel 100 by the vertical plane including the line
p-q in FIG. 15A, the state immediately before the liquid crystal
molecules vary is similar to the case of FIG. 7A as shown in FIG.
15B. Therefore, it results that the reverse tilt domain occurs also
on the upper right corner of the bright pixel.
[0170] On the right side of the bright pixel, the lateral
electrical field in a horizontal direction is generated in FIG. 15A
due to the adjacency with the black pixel located on the right
side. Although the horizontal direction is perpendicular to the
direction in which the liquid crystal molecules are biased to tilt
in accordance with the applied voltage, the liquid crystal
molecules become in the reverse tilt state temporally in advance
thereof due to the lateral electrical field exert a harmful
influence on the motion of other liquid crystal molecules biased to
tilt with the vertical electrical field. Therefore, the reverse
tilt domain occurs also on the right side of the bright pixel.
[0171] On the upper left corner of the bright pixel, the lateral
electrical field in an LU direction is generated in FIG. 15A due to
the adjacency with the upper left black pixel. Therefore, when
cutting the liquid crystal panel 100 by the vertical plane
including the line r-s in FIG. 15A, the state immediately before
the liquid crystal molecules vary is similar to the case of FIG. 7A
as shown in FIG. 15B. Therefore, it results that the reverse tilt
domain occurs also on the upper left corner of the bright pixel
similarly to the case of the right corner.
[0172] Further, on the left side of the bright pixel, the lateral
electrical field in a horizontal direction (X direction) is
generated due to the adjacency with the black pixel located on the
left side. Therefore, the reverse tilt domain occurs also on the
left side of the bright pixel similarly to the case of the right
side thereof.
[0173] It should be noted that since the lower side of the bright
pixel is the upstream side of the tilt azimuth direction in the
liquid crystal molecules, the liquid crystal molecules located on
the side bordering the black pixel on the lower side do not hinder
the motion of other liquid crystal molecules biased to tilt with
the vertical electrical field. Therefore, the reverse tilt domain
hardly occurs on the lower side of the bright pixel.
[0174] Therefore, in the case of considering that the tilt azimuth
angle .theta.b is equal to 0 degree in the normally black mode of
the VA type, it is conceivable that the reverse tilt domain can
occur in the bright pixel if the dark pixel is located on the upper
side, the right side, or the left side of the bright pixel in the
n-th frame.
[0175] Therefore, consideration will now be given from the
viewpoint of reducing the pixels constituting the display
departure.
[0176] Firstly, the case in which 9 pixels of 3.times.3 change due
to the movement of a black pattern as shown in FIG. 16 is assumed,
and at the same time, attention is focused on the pixel at the
center thereof. In this example, the observed pixel changes from
the state in which the liquid crystal molecules are unstable in the
(n-1)-th frame to the bright pixel (Wt) in the n-th frame, and at
the same time, the dark pixels (Bk) border on the upper side, the
upper right side, and the right side thereof. In this case,
although the reverse tilt domain occurs on the upper side and the
right side of the observed pixel due to the lateral electrical
field in the n-th frame, since the bright pixel is located on the
left side, and no lateral electrical field is generated, the
reverse tilt domain does not occur on the left side.
[0177] Therefore, in the example shown in FIG. 16, if the black
pattern in the n-th frame moves one pixel upward in the subsequent
frame, the reverse tilt generation area is linked with the reverse
tilt generation area extending on the right side in a vertical
direction, and if the black pattern moves one pixel rightward in
the subsequent frame, the reverse tilt generation area is linked
with the reverse tilt generation area extending on the upper side
in a horizontal direction. Thus, the reverse tilt generation area
continues over a plurality of pixels, and as a result, it becomes
visually conspicuous.
[0178] Incidentally, in the example shown in FIG. 16, how the
reverse tilt occurs in the observed pixel is similar to the case
having the tilt azimuth angle .theta.b of 45 degrees shown in FIG.
12A. Therefore, in the observed pixel, if the upper pixel is the
bright pixel, the reverse tilt domain does not occur on the upper
side, and similarly, if the right pixel is the bright pixel, the
reverse tilt domain does not occur on the right side.
[0179] Therefore, even in the case in which the tilt azimuth angle
.theta.b is 0 degree, if the pixel to be changed from the state in
which the liquid crystal molecules are unstable to the bright pixel
(Wt) is not surrounded with two sides (i.e., the upper side and the
right side) causing the lateral electrical field but is surrounded
with either one of such sides, the reverse tilt generation areas
are not linked with each other, but remain discrete, and therefore,
it is conceivable there is no chance to be visually
conspicuous.
[0180] Then, the case in which 9 pixels of 3.times.3 change due to
the movement of a black pattern as shown in FIG. 17 is assumed. In
this case, the observed pixel located at the center changes from
the state in which the liquid crystal molecules are unstable in the
(n-1)-th frame to the bright pixel (Wt) in the n-th frame, and at
the same time, the dark pixels (Bk) border on the upper side, the
upper left side, and the left side thereof. Therefore, although the
reverse tilt domain occurs on the upper side and the left side of
the observed pixel due to the lateral electrical field in the n-th
frame, the reverse tilt domain does not occur on the right side.
Therefore, in the example shown in FIG. 17, if the black pattern in
the n-th frame moves one pixel upward in the subsequent frame, the
reverse tilt generation area is linked with the reverse tilt
generation area extending on the left side in a vertical direction,
and if the black pattern moves one pixel leftward in the subsequent
frame, the reverse tilt generation area is linked with the reverse
tilt generation area extending on the upper side in a horizontal
direction. Thus, the reverse tilt generation area continues over a
plurality of pixels, and as a result, it becomes visually
conspicuous.
[0181] Incidentally, similarly in the case shown in FIG. 17, if the
observed pixel to be changed from the state in which the liquid
crystal molecules are unstable to the bright pixel (Wt) is not
surrounded with two sides (i.e., the upper side and the left side)
causing the lateral electrical field but is surrounded with either
one of such sides, the reverse tilt generation areas are not linked
with each other, but remain discrete, and therefore, it is
conceivable there is no chance to be visually conspicuous.
[0182] Therefore, it results that in the case in which the tilt
azimuth angle .theta.b is equal to 0 degree, it is sufficient to
perform the following process. That is, it results that it is
sufficient that, in the boundary on which the dark pixel and the
bright pixel border each other in the image represented by the
video signal Vid-in, the portion having the dark pixel located on
the upper side and the bright pixel located on the lower side, the
portion having the dark pixel located on the right side and the
bright pixel located on the left side, and the portion having the
dark pixel located on the left side and the bright pixel located on
the right side are detected as the risk boundary in the n-th frame,
and the process of applying the voltage with which the liquid
crystal molecules do not become in the unstable state to the liquid
crystal element of the dark pixel surrounded by the risk boundary
on at least two sides (i.e., the left side and the lower side, or
the right side and the lower side) out of the dark pixels abutting
on the risk boundary is performed. This is because the reverse tilt
can thus be prevented from occurring in the oncoming (n+1)-th
frame.
[0183] In order for achieving the above, it is sufficient to
perform the following process in the embodiment described above.
That is, it is sufficient to adopt the configuration in which the
risk boundary detection section 321 detects the portion having the
dark pixel located on the left side and the bright pixel located on
the right side in the second detection as the risk boundary in
addition to the portion having the dark pixel located on the upper
side and the bright pixel located on the lower side, and the
portion having the dark pixel located on the right side and the
bright pixel located on the left side in the boundary detected in
the first detection, and further, the specifying section 322
specifies the dark pixel surrounded by the risk boundary on two or
more sides out of the dark pixels abutting on the risk
boundary.
[0184] FIG. 18 is a diagram showing a specific example of the
process performed by the video processing circuit 30 in the case in
which the tilt azimuth angle .theta.b is equal to 0 degree in the
normally black mode of the VA type on the same pattern as shown in
FIG. 13. The correction section 300 determines the application
boundary shown in the part 4 of FIG. 18 based on the part 1 and
part 2 of FIG. 13, while the risk boundary detection section 321
detects the risk boundary.
[0185] The risk boundary to be detected is different from the case
shown in FIG. 14 in the point that the portion having the dark
pixel located on the left side and the bright pixel located on the
right side is also detected as the risk boundary, and the point
that the dark pixel surrounded by the risk boundary on the lower
side and the right side also becomes the object of the grayscale
level replacement.
[0186] It should be noted that although the dark pixel surrounded
by the risk boundary on three sides, namely the lower side, the
left side, and the right side, fails to be included in the example
shown in FIG. 18, such a dark pixel also becomes the object of the
grayscale level replacement.
[0187] In the case in which the tilt azimuth angle .theta.b is
equal to 0 degree, if there exists the portion changing from the
black pixel to the white pixel in accordance with the black pattern
composed of the black pixels moving one pixel in any direction
except the downward direction in the image defined by the video
signal Vid-in, it becomes possible for the liquid crystal panel 100
to prevent the reverse tilt domain from occurring because the
portion is not changed from the state in which the liquid crystal
molecules are unstable directly to the white pixel, but is changed
to the white pixel after once passing through the state in which
the liquid crystal molecules are forced to be stabilized due to the
application of the voltage Vc corresponding to the grayscale level
of "c1."
[0188] It should be noted that as described above, the reverse tilt
domain hardly occurs if the black pattern moves one pixel in the
downward direction.
Tilt Azimuth Angle: 225 Degrees
[0189] Then, the case in which the tilt azimuth angle .theta.b is
equal to 225 degree as shown in FIG. 19A will be explained. It
should be noted that since this example is equivalent to the case
of rotating the example of the case in which the tilt azimuth angle
.theta.b is equal to 45 degrees shown in FIGS. 9A through 9C as
much as 180 degrees, the generation area of the reverse tilt also
has the relationship of being flipped vertically and horizontally
about the center of the pixel as shown in FIG. 19B.
[0190] Therefore, it results that in the case in which the tilt
azimuth angle .theta.b is equal to 225 degrees, it is sufficient to
perform the following process. That is, it results that it is
sufficient that, in the boundary on which the dark pixel and the
bright pixel border each other in the image represented by the
video signal Vid-in, the portion having the dark pixel located on
the lower side and the bright pixel located on the upper side, and
the portion having the dark pixel located on the left side and the
bright pixel located on the right side are detected as the risk
boundary in the n-th frame, and the process of applying the voltage
with which the liquid crystal molecules do not become in the
unstable state to the liquid crystal element of the dark pixel
surrounded by the risk boundary on two sides (i.e., the upper side
and the right side) out of the dark pixels abutting on the risk
boundary is performed. This is because the reverse tilt can thus be
prevented from occurring in the oncoming (n+1)-th frame.
[0191] In order for achieving the above, it is sufficient to
perform the following process in the embodiment described above.
That is, it is sufficient to adopt the configuration in which the
risk boundary detection section 321 detects the portion having the
dark pixel located on the lower side and the bright pixel located
on the upper side, and the portion having the dark pixel located on
the left side and the bright pixel located on the right side in the
second detection as the risk boundary in the boundary detected in
the first detection, and further, the specifying section 322
specifies the dark pixel surrounded by the risk boundary on the two
sides out of the dark pixels abutting on the risk boundary.
[0192] FIG. 20 is a diagram showing a specific example of the
process performed by the video processing circuit 30 in the case in
which the tilt azimuth angle .theta.b is equal to 225 degrees in
the normally black mode of the VA type. The correction section 300
determines the application boundary shown in the part 4 of FIG. 20
based on the part 1 and part 2 of FIG. 13, while the risk boundary
detection section 321 detects the risk boundary. In comparison with
the case shown in FIG. 14, they are different in the risk boundary,
and the point that the dark pixel surrounded by the risk boundary
on the upper side and the right side becomes the object of the
grayscale level replacement. It should be noted that the advantages
are the same as those of the embodiment.
Pixels to be Object of Replacement
[0193] In the embodiment described above, there is adopted the
configuration of replacing the grayscale level of the dark pixel
set to be the object of the replacement with the grayscale level of
"c1" if the grayscale level darker than "c1" is designated to the
dark pixel. This is because the pixel in which the liquid crystal
molecules become in the unstable state due to the low application
voltage to the liquid crystal element in the normally black mode is
the dark pixel.
[0194] Incidentally, in order for preventing the reverse tilt
domain from occurring, it might be effective in some cases only to
reduce the lateral electrical field generated by the dark pixel and
the bright pixel located on both sides of the risk boundary.
[0195] Here, in order for reducing the lateral electrical field
generated by the dark pixel and the bright pixel, there can be
cited the process of correcting the bright pixel to be darker in
the normally black mode, and the process of correcting the dark
pixel and at the same time correcting the bright pixel to be
darker, besides the embodiment.
[0196] Therefore, these processes will be explained taking the case
in which the tilt azimuth angle .theta.b is equal to 45 degrees in
the normally black mode of the VA type as an example.
Case 1: Correction of Higher Voltage Pixel
[0197] Firstly, the case of correcting the bright pixel out of the
dark pixel and the bright pixel located on both sides of the risk
boundary, namely the pixel (the higher voltage pixel) having the
higher applied voltage to the liquid crystal element, will be
explained.
[0198] In this case, it is enough for the discrimination section
314 to discriminate whether or not the pixel represented by the
video signal Vid-d is the bright pixel located on the left side or
the lower side of the dark pixel specified by the specifying
section 322, set the value of the flag Q to "1" if the
discrimination result is "Yes," and set it to "0" if the
discrimination result is "No." Further, it is also possible in this
discrimination to set the value of the flag Q to "1" if the pixel
represented by the video signal Vid-d is the bright pixel located
on the lower left side of the dark pixel specified by the
specifying section 322, or to add the case in which the grayscale
level of the dark pixel specified by the specifying section 322 is
darker than "c1" to the requirements of the discrimination.
[0199] Further, it is possible to adopt the configuration in which
the grayscale level designated by the video signal Vid-d is
replaced with the level "c2" having a predetermined amount darker
if the value of the flag Q is "1" in the selector 312.
[0200] FIG. 21 is a diagram showing a specific example of the
process in the case of replacing the grayscale level of the higher
voltage pixel abutting on the risk boundary. The correction section
300 determines the application boundary shown in the part 4 of FIG.
21 based on the part 1 and part 2 of FIG. 13, while the risk
boundary detection section 321 detects the risk boundary. In
comparison with the case shown in FIG. 14, they are different in
the point that the pixel to be the object of the replacement is the
bright pixel located on the lower side and the left side of the
dark pixel (white circle) surrounded by the risk boundary on the
upper side and the right side, and the point that the grayscale
level of the bright pixel is replaced with the darker grayscale
level of "c2." Since according also to such a process the lateral
electrical field to be generated is modified to be smaller, it
becomes possible to prevent the reverse tilt domain from
occurring.
[0201] It should be noted that in the example shown in FIG. 21 it
is also possible to replace the grayscale level of the bright pixel
(.times. mark) located on the lower left side of the dark pixel
surrounded by the risk boundary on two sides with the grayscale
level of "c2."
Case 2: Bilateral Correction Including Higher Voltage Pixel
[0202] Subsequently, the case of correcting the dark pixel with a
darker level than the grayscale level "c1" and at the same time
correcting the bright pixel to be darker will be explained. The
correction section 300 determines the application boundary shown in
the part 4 of FIG. 22 based on the part 1 and part 2 of FIG. 13,
while the risk boundary detection section 321 detects the risk
boundary.
[0203] The processing result of the process of replacing the pixel
in the correction section 300 is the same as what is obtained by
performing both of the embodiment described above and the
correction of the higher voltage pixel. Therefore, as shown in the
part 6 of FIG. 22, the specific example of the process also
corresponds to the contents obtained by combining the part 6 of
FIG. 14 and the part 6 of FIG. 21.
[0204] Since according also to such a process the lateral
electrical field to be generated is modified to be smaller, it
becomes possible to prevent the reverse tilt domain from
occurring.
[0205] In particular, since in the present example the grayscale
levels of both of the dark pixel and the bright pixel are
corrected, the boundary between the dark pixel and the bright pixel
represented by the original video signal Vid-in is viewed as the
contour of the corrected image without modification. Therefore, in
the present example, it becomes possible to prevent the contour
information of the image represented by the original video signal
Vid-in from being lost by the correction.
[0206] It should be noted that in the case of correcting the
grayscale levels of both of the dark pixel and the bright pixel, it
is also possible to correct a plurality of pixels on the dark pixel
side in the direction of increasing the distance from the risk
boundary, and to correct a plurality of pixels on the bright pixel
side in the direction of increasing the distance from the risk
boundary as shown in the part 6 of FIG. 23. Further, in the case of
correcting the plurality of pixels on the dark pixel side in the
direction of increasing the distance from the risk boundary, it is
also possible to stop the correction on the bright pixel side.
TN Type
[0207] In the embodiment described above, the example of applying
the VA type to the liquid crystal 105 is explained. Therefore, an
example of applying the TN type to the liquid crystal 105 will
hereinafter be explained.
[0208] FIG. 24A is a diagram showing 2.times.2 pixels in the liquid
crystal panel 100, and FIG. 24B is a simplified cross-sectional
view when breaking the liquid crystal panel 100 with the vertical
plane including the line p-q shown in FIG. 24A.
[0209] It is assumed that as shown in these drawings, the liquid
crystal molecules of the TN type are initially oriented with the
tilt angle of 0a and the tilt azimuth angle of .theta.b (=45
degrees) in the state in which the electrical potential difference
between the pixel electrode 118 and the common electrode 108 is set
to zero. In the TN type, in contrast to the VA type, since the
liquid crystal molecules tilt in a direction parallel to the
substrate, the tilt angle .theta.a of the TN type has a value
larger than in the VA type.
[0210] In the example of applying the TN type to the liquid crystal
105, the normally white mode in which the liquid crystal element
120 becomes in the white state when no voltage is applied is used
in many cases on the ground, for example, that a higher contrast
ratio can be obtained.
[0211] Therefore, in the case of applying the TN type to the liquid
crystal 105, and adopting the normally white mode, the relationship
between the applied voltage and the transmittance of the liquid
crystal element 120 can be expressed by the V-T characteristics
shown in FIG. 4B, and the transmittance is reduced as the applied
voltage rises. It should be noted that there is no difference from
the normally black mode in the point that the liquid crystal
molecules become in the unstable state when the applied voltage to
the liquid crystal element 120 becomes lower than the voltage
Vc.
[0212] In such a normally white mode of the TN type, it is assumed
that the state of the four pixels of 2.times.2 changes from the
state in which all of the pixels are white pixels having the liquid
crystal molecules in the unstable state in the (n-1)-th frame to
the state in which the upper right pixel alone is the black pixel
in the n-th frame as shown in FIG. 25A.
[0213] As described above, in the normally white mode the
electrical potential difference between the pixel electrode 118 and
the common electrode 108 is larger in the black pixel than in the
white pixel in contrast to the normally black mode. Therefore, in
the upper right pixel to be changed from white to black, the liquid
crystal molecules are biased to rise in the direction (the normal
direction to the substrate surface) along the electrical field
direction from the state illustrated with solid lines to the state
illustrated with broken lines as shown in FIG. 25B.
[0214] However, the electrical potential difference generated in
the gap between the pixel electrode 118 (Wt) of the white pixel and
the pixel electrode 118 (Bk) of the black pixel is comparable to
the electrical potential difference generated between the pixel
electrode 118 (Bk) of the black pixel and the common electrode 108,
and moreover, the gap between the pixel electrodes is narrower than
the gap between the pixel electrode 118 and the common electrode
108. Therefore, in comparison in the intensity of the electrical
field, the lateral electrical field generated in the gap between
the pixel electrode 118 (Wt) and the pixel electrode 118 (Bk) is
stronger than the vertical electrical field generated between the
pixel electrode 118 (Bk) and the common electrode 108.
[0215] Since the upper right pixel has been the white pixel with
the liquid crystal molecules in the unstable state in the (n-1)-th
frame, it takes time until the liquid crystal molecules rise in
accordance with the intensity of the vertical electrical field. On
the other hand, since the lateral electrical field with the
adjacent pixel electrode 118 (Wt) is stronger than the vertical
electrical field caused by applying the voltage in the black level
to the pixel electrode 118 (Bk), the liquid crystal molecules Rv on
the side abutting on the white pixel become in the reverse tilt
state in the pixel biased to be changed to the black pixel as shown
in FIG. 25B temporally prior to other liquid crystal molecules
biased to rise in accordance with the vertical electrical
field.
[0216] The liquid crystal molecules Rv having become in the reverse
tilt state earlier affect negatively the motion of other liquid
crystal molecules biased to rise in the direction perpendicular to
the substrate as illustrated with the broken lines in accordance
with the vertical electrical field. Therefore, the area where the
reverse tilt occurs in the pixel to be changed to the black pixel
spreads across the wide area beyond the gap between the pixel to be
changed to the black pixel and the white pixel so as to eat into
the pixel to be changed to the black pixel as shown in FIG.
25C.
[0217] Therefore, it results that if the peripheral pixels of the
observed pixel to be changed to the black pixel are the white
pixels, in the case in which the white pixels abut on the observed
pixel on the lower left side, the left side, and the lower side,
the reverse tilt domain occurs in the observed pixel on the left
side and the lower side.
[0218] Incidentally, it is assumed that the state of the four
pixels of 2.times.2 changes from the state in which all of the
pixels are white pixels having the liquid crystal molecules in the
unstable state in the (n-1)-th frame to the state in which the
lower left pixel alone is the black pixel in the n-th frame as
shown in FIG. 26A. Even in the change described above, the lateral
electrical field stronger than the vertical electrical field in the
gap between the pixel electrode 118 (Bk) and the common electrode
108 is generated in the gap between the pixel electrode 118 (Bk) of
the black pixel and the pixel electrode 118 (Wt) of the white
pixel. Due to the lateral electrical field, as shown in FIG. 26B,
in the white pixel, the liquid crystal molecules Rv located on the
side adjacent to the black pixel are varied in the orientation
temporally prior to other liquid crystal molecules biased to rise
in accordance with the vertical electrical field, and thus become
in the reverse tilt state. However, in the white pixel, since the
intensity of the vertical electrical field does not vary from the
(n-1)-th frame, other liquid crystal molecules are hardly affected.
Therefore, as shown in FIG. 26C, the area where the reverse tilt
occurs in the pixel not changing from the white pixel is negligibly
narrow compared to the example shown in FIG. 25C.
[0219] Further, in the lower left pixel out of the four pixels of
2.times.2, which changes from white to black, since the initial
orientation direction of the liquid crystal molecules is the
direction hardly affected by the lateral electrical field, the
liquid crystal molecules becoming in the reverse tilt state hardly
exist even if the vertical electrical field is applied. Therefore,
in the lower left pixel, the liquid crystal molecules correctly
rise in the direction perpendicular to the substrate as illustrated
with the broken lines in FIG. 26B as the intensity of the vertical
electrical field increases. As a result, since the lower left pixel
changes to the aimed black pixel, deterioration of the display
quality hardly occurs.
[0220] In conclusion, in the case in which the tilt azimuth angle
.theta.b is equal to 45 degrees in the normally white mode of the
TN type, the reverse tilt domain is similar to the case (see FIGS.
19A, 19B, and 20) in which the tilt azimuth angle .theta.b is equal
to 225 degrees in the normally black mode of the VA type except the
fact that the relationship (V-T characteristics) of black and white
with respect to the voltage is reversed.
[0221] Therefore, in the case in which the tilt angle .theta.b is
equal to 45 degrees in the TN type, in view of reducing the pixels
constituting the display departure, the following can be obtained
from the content shown in FIGS. 27A and 27B, and the analogy of the
VA type.
[0222] That is, in the case in which the tilt azimuth angle
.theta.b is equal to 45 degrees in the normally white mode of the
TN type, it is sufficient that, in the boundary on which the bright
pixel (the lower voltage pixel) and the dark pixel (the higher
voltage pixel) border each other in the image represented by the
video signal Vid-in, the portion having the bright pixel located on
the upper side and the dark pixel located on the lower side, and
the portion having the bright pixel located on the right side and
the dark pixel located on the left side are detected as the risk
boundary in the n-th frame, and the process of applying the voltage
with which the liquid crystal molecules do not become in the
unstable state to the liquid crystal element of the bright pixel
surrounded by the risk boundary on two sides (i.e., the upper side
and the right side) out of the bright pixels abutting on the risk
boundary is performed.
[0223] It should be noted that although in the present example the
example of setting the tilt azimuth angle .theta.b to 45 degrees in
the normally white mode of the TN type is explained, taking the
point that generation direction of the reverse tilt domain is
reversed from the VA type and the point that the V-T
characteristics are different into consideration, it must be
possible to easily obtain the measures for the case in which the
tilt azimuth angle .theta.b is not equal to 45 degrees and the
configuration therefor by the analogy of the above explanation.
[0224] In the explanation described above, although it is assumed
that the video signal Vid-in designates the grayscale levels of the
pixels, it is also possible to assume that the video signal Vid-in
directly designates the applied voltages to the liquid crystal
elements. In the case in which the video signal Vid-in designates
the applied voltages to the liquid crystal elements, it is
sufficient to adopt the configuration of discriminating the
boundary based on the applied voltage thus designated to thereby
correct the voltage.
[0225] Further, the liquid crystal element 120 is not limited to
the transmissive type, but can be of the reflective type.
[0226] Further, although the image is for expressing the grayscale
from white to black, it is also possible to adopt the configuration
of expressing the color of one dot with three pixels respectively
colored by the color filter of red (R), green (G), and blue (B),
for example. It should be noted that the projector hereinafter
explained is for forming the color image by combining the primary
color images respectively generated by the three liquid crystal
panels.
Electronic Apparatus
[0227] Then, as an example of the electronic apparatus using the
liquid crystal display device according to the embodiment described
above, a projector using the liquid crystal panels 100 as the light
valves will be explained. FIG. 28 is a plan view showing the
configuration of the projector.
[0228] As shown in the drawing, a lamp unit 2102 composed mainly of
a white light source such as a halogen lamp is disposed inside the
projector 2100. A projection light beam emitted from the lamp unit
2102 is separated into three primary colors of R (red), G (green),
and B (blue) by three mirrors 2106 and two dichroic mirrors 2108
disposed inside thereof, and then respectively guided to the light
valves 100R, 100G, and 100B corresponding to the respective primary
colors. It should be noted that since the B color light beam has a
longer light path compared to the other colors, the R color and G
color, and is therefore guided via a relay lens system 2121
composed of an entrance lens 2122, a relay lens 2123, and an exit
lens 2124 in order for preventing the loss.
[0229] In the projector 2100, the three sets of liquid crystal
display devices each including the liquid crystal panel 100
correspond respectively to the R color, G color, and B color. The
configuration of each of the light valves 100R, 100G, and 100B is
substantially the same as that of the liquid crystal panel 100
described above. There is adopted the configuration in which the
video signals for designating the grayscale levels of the
respective primary color components of R color, G color, and B
color are supplied from respective external higher-level circuits,
and the light valves 1008, 100G, and 100B are driven
respectively.
[0230] The light beams respectively modulated by the light valves
100R, 100G, and 100B enter the dichroic prism 2112 in three
directions. Then, in the dichroic prism 2112, the light beams of
the R color and B color are refracted 90 degrees while the light
beam of the G color goes straight.
[0231] Therefore, it results that after the images of the
respective primary colors are combined, the color image is
projected by the projection lens 2114 to the screen 2120.
[0232] It should be noted that since the light beams corresponding
respectively to the primary colors of the R color, G color, and B
color enter the light valves 1008, 100G, and 100B due to the
dichroic mirrors 2108, no color filter is required to be disposed.
Further, since the transmission images of the light valves 100R,
100B are reflected by the dichroic prism 2112 and then projected
while the transmission image of the light valve 100G is projected
directly, there is adopted the configuration in which the
horizontal scanning direction of the light valves 100R, 100B is set
to the reverse direction of the horizontal scanning direction of
the light valve 100G to thereby display the horizontally mirror
reversed images.
[0233] As an example of applying the liquid crystal panel 100 to
the light valve, there can be cited a television set of the rear
projection type besides the projector explained above with
reference to FIG. 28. Further, the liquid crystal panel 100 can
also be applied to a mirror-less interchangeable lens camera, an
electronic view finder (EVF) in a video camera, and so on.
[0234] Besides the above, as an applicable electronic apparatus,
there can be cited a head mount display, a car navigation system, a
pager, an electronic organizer, an electronic calculator, a word
processor, a workstation, a picture phone, a POS terminal, a
digital still camera, a cellular phone, an apparatus equipped with
a touch panel, and so on. Further, it is obvious that the liquid
crystal display device described above can be applied to the
various types of electronic apparatuses cited above.
[0235] The entire disclosure of Japanese Patent Application No.
2010-039795, filed Feb. 25, 2010 is expressly incorporated by
reference herein.
* * * * *